Publications

@article{WOS:001622155800001,

title = {X-ray analysis of 

 Mg0.2Co0.2Ni0.2Cu0.2Zn0 

 .2O: disentangling elemental contributions in a prototypical 

 high-entropy oxide},

author = {Maryia Zinouyeva and Martina Fracchia and Giulia Maranini and Mauro Coduri and Davide Impelluso and Nicholas B. Brookes and Lorenzo Grilli and Kurt Kummer and Francesco Rosa and Matteo Aramini and Giacomo Ghiringhelli and Paolo Ghigna and Marco Moretti Sala},

doi = {10.1039/d5ta05324b},

issn = {2050-7488},

year  = {2026},

date = {2026-01-01},

journal = {JOURNAL OF MATERIALS CHEMISTRY A},

volume = {14},

number = {2},

pages = {1221-1233},

publisher = {ROYAL SOC CHEMISTRY},

address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, 

 ENGLAND},

abstract = {We employ several X-ray based techniques, including X-ray diffraction, 

 X-ray absorption spectroscopy and resonant inelastic X-ray scattering, 

 to disentangle the contributions of individual chemical species to the 

 structural, electronic and magnetic properties of high-entropy oxides. 

 In the benchmark compound Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O and related 

 systems, we unambiguously resolve a sizable Jahn-Teller distortion at 

 the Cu sites, more pronounced in the absence of Ni2+ and Mg2+, 

 suggesting that these ions promote positional order, whereas Cu2+ ions 

 act to destabilize it. Moreover, we detect magnetic excitations and 

 estimate the strength of the interactions between pairs of different 

 magnetic elements. Our results provide valuable insights into the role 

 of various chemical species in shaping the physical properties of 

 high-entropy oxides.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:001648158900001,

title = {Exploring Low Energy Excitations in the d5 Iridate Double Perovskites La2BIrO6 (B = Zn, 

 Mg)},

author = {Abhisek Bandyopadhyay and Dheeraj Kumar Pandey and Carlo Meneghini and Anna Efimenko and Marco Moretti Sala and Sugata Ray},

doi = {10.3390/condmat10040053},

issn = {2410-3896},

year  = {2025},

date = {2025-10-01},

journal = {CONDENSED MATTER},

volume = {10},

number = {4},

publisher = {MDPI},

address = {MDPI AG, Grosspeteranlage 5, CH-4052 BASEL, SWITZERLAND},

abstract = {We experimentally investigate the structural, magnetic, transport, and 

 electronic properties of two d(5) iridate double perovskite materials La2BIrO6 (B = Mg, Zn). Notably, despite similar crystallographic 

 structure, the two compounds show distinctly different magnetic behaviors. The M = Mg compound shows an antiferromagnetic-like linear 

 field-dependent isothermal magnetization below its transition temperature, whereas the M = Zn counterpart displays a clear hysteresis 

 loop followed by a noticeable coercive field, indicative of 

 ferromagnetic components arising from a non-collinear Ir spin 

 arrangement. The local structure studies authenticate perceptible M/Ir 

 antisite disorder in both systems, which complicates the magnetic 

 exchange interaction scenario by introducing Ir-O-Ir superexchange 

 pathways in addition to the nominal Ir-O-B-O-Ir super-superexchange 

 interactions expected for an ideally ordered structure. While spin-orbit 

 coupling (SOC) plays a crucial role in establishing insulating behavior 

 for both these compounds, the rotational and tilting distortions of the 

 IrO6 (and MO6) octahedral units further lift the ideal cubic symmetry. 

 Finally, by measuring the Ir-L-3 edge resonant inelastic X-ray 

 scattering (RIXS) spectra for both the compounds, giving evidence of 

 spin-orbit-derived low-energy inter-J-state (intra t(2g)) transitions 

 (below similar to 1 eV), the charge transfer (O 2p -> Ir 5d), and the 

 crystal field (Ir t(2g) -> e(g)) excitations, we put forward a 

 qualitative argument for the interplay among effective SOC, non-cubic 

 crystal field, and intersite hopping in these two compounds.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Sahib2025,

title = {Superconductivity in PrNiO2 Infinite-Layer Nickelates},

author = {Hoshang Sahib and Aravind Raji and Francesco Rosa and Giacomo Merzoni and Giacomo Ghiringhelli and Marco Salluzzo and Alexandre Gloter and Nathalie Viart and Daniele Preziosi},

doi = {10.1002/adma.202416187},

issn = {0935-9648},

year  = {2025},

date = {2025-04-01},

journal = {ADVANCED MATERIALS},

volume = {37},

number = {16},

publisher = {WILEY-V C H VERLAG GMBH},

address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY},

abstract = {Several reports about infinite-layer nickelate thin films suggest that 

 the superconducting critical temperature versus chemical doping phase 

 diagram has a dome-like shape, similar to cuprates. Here, a highly 

 reproducible superconducting state in undoped PrNiO2 thin films grown on 

 SrTiO3 are demonstrated. Scanning transmission electron microscopy 

 measurements show coherent infinite-layer phase with no visible 

 stacking-fault defects, an overall high structural quality where 

 possible unintentional chemical doping or interstitial oxygen, if 

 present, sum well below the measurable threshold of the technique. X-ray 

 absorption measurements show very sharp features at the Ni L-3,L-2-edges 

 with a large linear dichroism, indicating the preferential hole 

 occupation of Ni1+-3d(x)(2)-y(2) orbitals in a square planar geometry. 

 Resonant inelastic X-ray scattering measurements reveal sharp magnon 

 excitations of 200 meV energy at the magnetic Brillouin zone boundary, 

 highly resonant at the Ni1 + absorption peak. The results indicate that, 

 when properly stabilized, infinite-layer nickelate thin films are 

 superconducting without chemical doping.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:001448959600010,

title = {Quasimolecular electronic structure of the trimer iridate Ba4NbIr3O12},

author = {M. Magnaterra and A. Sandberg and H. Schilling and L. Paetzold and P. Warzanowski and E. Bergamasco and Ch. J. Sahle and B. Detlefs and K. Ruotsalainen and M. Moretti Sala and G. Monaco and P. Becker and Q. Faure and G. S. Thakur and M. Songvilay and C. Felser and P. H. M. van Loosdrecht and J. Brink and M. Hermanns and M. Grueninger},

doi = {10.1103/PhysRevB.111.085122},

issn = {2469-9950},

year  = {2025},

date = {2025-02-01},

journal = {PHYSICAL REVIEW B},

volume = {111},

number = {8},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {The insulating mixed-valent Ir+3.66 compound Ba4NbIr3O12 hosts two holes 

 per Ir3O12 trimer unit. We address the electronic structure via resonant 

 inelastic x-ray scattering (RIXS) at the Ir L3 edge and exact 

 diagonalization. The holes occupy quasimolecular orbitals that are 

 delocalized over a trimer. This gives rise to a rich intra-t2g 

 excitation spectrum that extends from 0.5 eV to energies larger than 2 

 eV. Furthermore, it yields a strong modulation of the RIXS intensity as 

 a function of the transferred momentum q. A clear fingerprint of the 

 quasimolecular trimer character is the observation of two modulation 

 periods, 27r /d and 27r /2d, where d and 2d denote the intratrimer Ir-Ir 

 distances. We discuss how the specific modulation reflects the character 

 of the wave function of an excited state. Our quantitative analysis 

 shows that spin-orbit coupling ) of about 0.4 eV is decisive for the 

 character of the electronic states, despite a large hopping ta1g of 

 about 0.8 eV. The ground state of a single trimer is described very well by both holes occupying the bonding j = 12 orbital, forming a vanishing quasimolecular moment with J = 0.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Schlappa2025,

title = {The Heisenberg-RIXS instrument at the European XFEL},

author = {Justine Schlappa and Giacomo Ghiringhelli and Benjamin E. Van Kuiken and Martin Teichmann and Piter S. Miedema and Jan Torben Delitz and Natalia Gerasimova and Serguei Molodtsov and Luigi Adriano and Bernard Baranasic and Carsten Broers and Robert Carley and Patrick Gessler and Nahid Ghodrati and David Hickin and Le Phuong Hoang and Manuel Izquierdo and Laurent Mercadier and Giuseppe Mercurio and Sergii Parchenko and Marijan Stupar and Zhong Yin and Leonardo Martinelli and Giacomo Merzoni and Ying Ying Peng and Torben Reuss and Sreeju Sreekantan Nair Lalithambika and Simone Techert and Tim Laarmann and Simo Huotari and Christian Schroeter and Burkhard Langer and Tatjana Giessel and Jana Buchheim and Grzegorz Gwalt and Andrey Sokolov and Frank Siewert and Robby Buechner and Vinicius Vaz Cruz and Sebastian Eckert and Chun-Yu Liu and Christian Sohrt and Christian Weniger and Annette Pietzsch and Stefan Neppl and Friedmar Senf and Andreas Scherz and Alexander Foehlisch},

doi = {10.1107/S1600577524010890},

issn = {0909-0495},

year  = {2025},

date = {2025-01-01},

journal = {JOURNAL OF SYNCHROTRON RADIATION},

volume = {32},

number = {1},

pages = {29-45},

publisher = {INT UNION CRYSTALLOGRAPHY},

address = {2 ABBEY SQ, CHESTER, CH1 2HU, ENGLAND},

abstract = {Resonant inelastic X-ray scattering (RIXS) is an ideal X-ray 

 spectroscopy method to push the combination of energy and time 

 resolutions to the Fourier transform ultimate limit, because it is 

 unaffected by the core-hole lifetime energy broadening. Also, in 

 pump-probe experiments the interaction time is made very short by the 

 same core-hole lifetime. RIXS is very photon hungry so it takes great 

 advantage from high-repetition-rate pulsed X-ray sources like the 

 European XFEL. The Heisenberg RIXS instrument is designed for RIXS 

 experiments in the soft X-ray range with energy resolution approaching 

 the Fourier and the Heisenberg limits. It is based on a spherical 

 grating with variable line spacing and a position-sensitive 2D detector. 

 Initially, two gratings were installed to adequately cover the whole 

 photon energy range. With optimized spot size on the sample and small 

 pixel detector the energy resolution can be better than 40 meV (90 meV) 

 at any photon energy below 1000 eV with the high-resolution 

 (high-transmission) grating. At the SCS instrument of the European XFEL 

 the spectrometer can be easily positioned thanks to air pads on a 

 high-quality floor, allowing the scattering angle to be continuously 

 adjusted over the 65-145. range. It can be coupled to two different 

 sample interaction chambers, one for liquid jets and one for solids, 

 each state-of-the-art equipped and compatible for optical laser pumping 

 in collinear geometry. The measured performances, in terms of energy 

 resolution and count rate on the detector, closely match design 

 expectations. The Heisenberg RIXS instrument has been open to public 

 users since the summer of 2022.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:001389476000009,

title = {Spin excitations in Nd1-xSrxNiO2 and YBa2Cu3O7-δ: The influence of 

 Hubbard U},

author = {F. Rosa and L. Martinelli and G. Krieger and L. Braicovich and N. B. Brookes and G. Merzoni and M. Moretti Sala and F. Yakhou-Harris and R. Arpaia and D. Preziosi and M. Salluzzo and M. Fidrysiak and G. Ghiringhelli},

doi = {10.1103/PhysRevB.110.224431},

issn = {2469-9950},

year  = {2024},

date = {2024-12-01},

journal = {PHYSICAL REVIEW B},

volume = {110},

number = {22},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {We use resonant inelastic x-ray scattering (RIXS) to compare the doping 

 dependence of magnetic excitations of an infinite-layer nickelate to 

 those of a prototypical superconducting cuprate. The polarization 

 analysis of RIXS spectra establishes the dominant spin-flip nature of 

 the midinfrared peak in both cases. Hole doping leads to opposite 

 behavior of the magnetic energy in the two materials. By fitting the 

 data with an original Hubbard-based model for dynamic susceptibility, we 

 find that t is comparable in the two materials while U is about twice 

 larger in the nickelate. This finding accounts for the smaller magnetic 

 bandwidth of nickelates and for its decrease upon doping.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Krieger2024,

title = {Signatures of canted antiferromagnetism in infinite-layer nickelates studied by x-ray magnetic dichroism},

author = {G. Krieger and H. Sahib and F. Rosa and M. Rath and Y. Chen and A. Raji and P. V. B. Pinho and C. Lefevre and G. Ghiringhelli and A. Gloter and N. Viart and M. Salluzzo and D. Preziosi},

doi = {10.1103/PhysRevB.110.195110},

issn = {2469-9950},

year  = {2024},

date = {2024-11-01},

journal = {PHYSICAL REVIEW B},

volume = {110},

number = {19},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {We report an experimental study of the magnetic properties of infinite-layer Nd1-xSrxNiO2 (x = 0 and 0.2) thin films by x-ray magnetic 

 circular dichroism (XMCD) at Ni L3,2 and Nd M5,4 edges. We show the 

 presence of a field induced out-of-plane Ni1+ spin moment, reaching 

 values of 0.25 mu B/Ni at 9 T in the case of superconducting 

 Nd0.8Sr0.2NiO2. The magnetic field and temperature dependencies of the 

 Ni L3,2 XMCD data can be explained by an out-of-plane canting of 

 in-plane anti-ferromagnetically correlated Ni1+ spins. The canting is 

 most likely attributed to the symmetry lowering of the NiO2 planes, 

 observed via four-dimensional scanning transmission electron microscopy, 

 which can trigger a Dzyaloshinskii-Moriya interaction among the Ni1+ 

 spins.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:001355878400003,

title = {Spin orbital lattice entanglement in the ideal j=12 compound 

 K2IrCl6},

author = {P. Warzanowski and M. Magnaterra and Ch. J. Sahle and M. Moretti Sala and P. Becker and L. Bohaty and I. Cisarova and G. Monaco and T. Lorenz and P. H. M. Loosdrecht and J. Brink and M. Grueninger},

doi = {10.1103/PhysRevB.110.195120},

issn = {2469-9950},

year  = {2024},

date = {2024-11-01},

journal = {PHYSICAL REVIEW B},

volume = {110},

number = {19},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {Mott insulators with spin-orbit entangled j = 1/2 moments host intriguing magnetic properties. The j = 1/2 wave function requires cubic symmetry, while a noncubic crystal field mixes j = 1/2 and 3/2 

 character. Spectroscopic studies of 5d5 iridates typically claim noncubic symmetry, e.g., based on a splitting of the excited j = 3/2 

 quartet. A sizable splitting is particularly puzzling in 

 antifluorite-type K2IrCl6, a frustrated fcc quantum magnet with global 

 cubic symmetry. It raises the fundamental question about the stability of j = 1/2 moments against magnetoelastic coupling. Combining resonant 

 inelastic x-ray scattering with optical spectroscopy, we demonstrate 

 that the multi-peak line shape in K2IrCl6 reflects a vibronic character of the j = 3/2 states rather than a noncubic crystal field. The 

 quasimolecular crystal structure with well separated IrCl6 octahedra 

 explains the existence of well-defined sidebands that are usually 

 smeared out in solids. Our results highlight the spin orbital lattice entangled character of cubic K2IrCl6 with ideal j = 1/2 moments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:001276920000001,

title = {Disordered magnetic ground state in a quasi-1-D d4 

 columnar iridate Sr3LiIrO6},

author = {Abhisek Bandyopadhyay and Debu Das and A. Chakraborty and S. Bhowal and Vinod Kumar and G. B. G. Stenning and C. Ritter and D. T. Adroja and M. Moretti Sala and A. Efimenko and C. Meneghini and F. Bert and P. K. Biswas and I Dasgupta and T. Saha Dasgupta and A. V Mahajan and Sugata Ray},

doi = {10.1088/1361-648X/ad63eb},

issn = {0953-8984},

year  = {2024},

date = {2024-10-01},

journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},

volume = {36},

number = {42},

publisher = {IOP Publishing Ltd},

address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND},

abstract = {Spin-orbit coupling offers a large variety of novel and extraordinary 

 magnetic and electronic properties in otherwise `ordinary pool' of heavy 

 ion oxides. Here we present a detailed study on an apparently isolated 

 hexagonal 2H spin-chain d(4) iridate Sr3LiIrO6 with geometric 

 frustration. Our structural studies reveal Li-Ir chemical order with 

 desired stoichiometry in this compound, while x-ray absorption together 

 with x-ray photoemission spectroscopic characterizations establish pure 

 5+ valence of Ir. We have established a magnetic ground state with 

 finite Ir5+ magnetic moments in this compound, contrary to the anticipated nonmagnetic J(eff) = 0 state, through combined dc 

 susceptibility, 7Li nuclear magnetic resonance (NMR), muon spin 

 relaxation (mu SR) and ab-initio electronic structure studies. These 

 investigations together with ac magnetic susceptibility and specific 

 heat measurements reveal that despite having noticeable 

 antiferromagnetic correlation among the Ir5+ local moments, this system 

 does not magnetically order down to at least 0.05 K, possibly due to 

 geometrical exchange frustration, arising from the comparable nearest- 

 and next-nearest-neighbor interchain Ir-O-O-Ir superexchange interaction 

 strengths with opposite signs. However, the zero-field mu SR analysis 

 shows emergence of a considerable proportion of spin-freezing on top of 

 a spin-fluctuating dynamic magnetic background down to the lowest 

 measured temperature of 1.7 K, possibly due to some inhomogeneity and/or 

 the much stronger intra-column Ir-Ir magnetic exchange interaction 

 strength relative to the inter-column Ir-Ir ones. The linear temperature 

 dependence of the magnetic specific heat (C-m) in both zero and applied 

 magnetic fields, plus the power-law behavior of the NMR spin-lattice 

 relaxation rate suggest a gapless spinon density of states in this 

 charge gapped disordered magnetic ground state of Sr3LiIrO6.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:001288063900004,

title = {Origin of Magnetism in a Supposedly Nonmagnetic Osmium Oxide},

author = {S. Agrestini and F. Borgatti and P. Florio and J. Frassineti and D. Fiore Mosca and Q. Faure and B. Detlefs and C. J. Sahle and S. Francoual and J. Choi and M. Garcia-Fernandez and K. -j. Zhou and V. F. Mitrovic and P. M. Woodward and G. Ghiringhelli and C. Franchini and F. Boscherini and S. Sanna and M. Moretti Sala},

doi = {10.1103/PhysRevLett.133.066501},

issn = {0031-9007},

year  = {2024},

date = {2024-08-01},

journal = {PHYSICAL REVIEW LETTERS},

volume = {133},

number = {6},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {A supposedly nonmagnetic 5d1 double perovskite oxide is investigated by 

 a combination of spectroscopic and theoretical methods, namely, resonant 

 inelastic x-ray scattering, x-ray absorption spectroscopy, magnetic 

 circular dichroism, and multiplet ligand-field calculations. We found 

 that the large spin-orbit coupling admixes the 5d t2g and eg orbitals, 

 covalency raises the 5d population well above the nominal value, and the 

 local symmetry is lower than Oh. The obtained electronic interactions 

 account for the finite magnetic moment of Os in this compound and, in 

 general, of 5d1 ions. Our results provide direct evidence of elusive 

 Jahn-Teller distortions, hinting at a strong electron-lattice coupling.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:001230578500001,

title = {ID20-opportunities for inelastic X-ray scattering at extreme conditions},

author = {Christoph J. Sahle and Sylvain Petitgirard and Georg Spiekermann and Robin Sakrowski and Noora Suomalainen and Florent Gerbon and Jeroen Jacobs and Yves Watier and Christian Sternemann and Marco Moretti Sala and Valerio Cerantola},

doi = {10.1080/08957959.2024.2356523},

issn = {0895-7959},

year  = {2024},

date = {2024-07-01},

journal = {HIGH PRESSURE RESEARCH},

volume = {44},

number = {3, SI},

pages = {337-360},

publisher = {TAYLOR & FRANCIS LTD},

address = {2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND},

abstract = {Owing to the availability of bright X-rays sources such as the ESRF-EBS, 

 inelastic X-ray scattering of samples contained in complex sample 

 environments, including high pressure devices, has become feasible. 

 Compared to well-established characterization techniques such as X-ray 

 diffraction or X-ray absorption fine structure spectroscopy, inelastic 

 X-ray scattering of samples under extreme conditions is a relatively 

 novel probe. However, unique information about the electronic, magnetic, 

 and local atomic structure is accessible with inelastic X-ray 

 scattering. Here, capabilities of beamline ID20 of the ESRF in the field 

 of high pressure inelastic X-ray scattering are presented and some 

 recent activities are reviewed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:001238786900011,

title = {Charge response function probed by resonant inelastic x-ray scattering: 

 Signature of electronic gaps of 

 YBa2Cu3O7-δ},

author = {Giacomo Merzoni and Leonardo Martinelli and Lucio Braicovich and Nicholas B. Brookes and Floriana Lombardi and Francesco Rosa and Riccardo Arpaia and Marco Moretti Sala and Giacomo Ghiringhelli},

doi = {10.1103/PhysRevB.109.184506},

issn = {2469-9950},

year  = {2024},

date = {2024-05-01},

journal = {PHYSICAL REVIEW B},

volume = {109},

number = {18},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {In strongly correlated systems, the complete determination of the 

 dynamical susceptibility chi(q, omega) is of special relevance because 

 of the entwinement of the spin and charge components. Although resonant 

 inelastic x-ray scattering (RIXS) spectra are directly related to both 

 the charge [chi `'(c)(q, omega)] and the spin [chi `'(s)(q, omega)] 

 contributions, only the latter has been extensively studied with RIXS so 

 far. Here we show how to extract from RIXS spectra of high-T-c 

 superconducting cuprates relevant properties of chi `'(c), such as the 

 presence of the superconducting gap and of the pseudogap. In particular, 

 we exploit the temperature dependence of the Cu L-3 edge RIXS spectra of 

 underdoped YBa2Cu3O7-delta at specific wave vectors q. The signature of 

 the two gaps is given by the departure of the low-energy excitation 

 continuum from the Bosonic thermal evolution. This approach can be 

 immediately used to investigate systematically the nature of the 

 pseudogap in cuprates, thereby taking advantage of the RIXS technique 

 that does not suffer the limitations of surface-sensitive electron 

 spectroscopies. Its extension to other interesting materials is 

 foreseen.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ghiringhelli2024,

title = {A noticeable absence},

author = {Giacomo Ghiringhelli},

doi = {10.1038/s41563-024-01835-x},

issn = {1476-1122},

year  = {2024},

date = {2024-04-01},

journal = {NATURE MATERIALS},

volume = {23},

number = {4},

pages = {443-444},

publisher = {NATURE PORTFOLIO},

address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY},

abstract = {Better control over the quality of materials dissipates doubts about 

 charge order in infinite-layer nickelates and indicates that a 

 previously observed superstructure is probably a spurious effect related 

 to other crystalline phases. This finding strengthens the similarities 

 between nickelates and cuprates.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:001229774400001,

title = {Spin-orbit coupling in a half-filled t 2 g shell: The case 

 of 5 d 3 K 2 ReCl 6},

author = {P. Warzanowski and M. Magnaterra and G. Schlicht and Q. Faure and Ch. J. Sahle and P. Becker and L. Bohaty and M. Moretti Sala and G. Monaco and M. Hermanns and P. H. M. Loosdrecht and M. Gruninger},

doi = {10.1103/PhysRevB.109.155149},

issn = {2469-9950},

year  = {2024},

date = {2024-04-01},

journal = {PHYSICAL REVIEW B},

volume = {109},

number = {15},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {The half-filled t 2 g shell of the t 3 2 g configuration usually, in LS coupling, hosts a S = 3 / 2 ground state with quenched orbital moment. 

 This state is not Jahn-Teller active. Sufficiently large spin-orbit 

 coupling zeta has been predicted to change this picture by mixing in 

 orbital moment, giving rise to a sizable Jahn-Teller distortion. In 5 d 

 3 K 2 ReCl 6 we study the electronic excitations using resonant 

 inelastic x-ray scattering and optical spectroscopy. We observe on-site 

 intra- t 2 g excitations below 2 eV and corresponding overtones with two 

 intra- t 2 g excitations on adjacent sites, the Mott gap at 2.7 eV, t 2 

 g -to- e g excitations above 3 eV, and charge-transfer excitations at 

 still higher energy. The intra- t 2 g excitation energies are a 

 sensitive measure of zeta and Hund's coupling J H . The sizable value of 

 zeta approximate to 0 . 29 eV places K 2 ReCl 6 into the intermediate 

 coupling regime, but zeta/ J H approximate to 0 . 6 is not sufficiently 

 large to drive a pronounced Jahn-Teller effect. We discuss the ground state wave function in a Kanamori picture and find that the S = 3 / 2 

 multiplet still carries about 97% of the weight. However, the finite 

 admixture of orbital moment allows for subtle effects. We discuss small 

 temperature-induced changes of the optical data and find evidence for a 

 lowering of the ground state by about 3 meV below the structural phase 

 transitions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Martinelli2024b,

title = {Collective Nature of Orbital Excitations in Layered Cuprates in the Absence of Apical Oxygens},

author = {Leonardo Martinelli and Krzysztof Wohlfeld and Jonathan Pelliciari and Riccardo Arpaia and Nicholas B. Brookes and Daniele Di Castro and Mirian G. Fernandez and Mingu Kang and Yoshiharu Krockenberger and Kurt Kummer and Daniel E. McNally and Eugenio Paris and Thorsten Schmitt and Hideki Yamamoto and Andrew Walters and Ke-Jin Zhou and Lucio Braicovich and Riccardo Comin and Marco Moretti Sala and Thomas P. Devereaux and Maria Daghofer and Giacomo Ghiringhelli},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85184856519&doi=10.1103%2fPhysRevLett.132.066004&partnerID=40&md5=0b788da6d9f31c5708086307160483dc},

doi = {10.1103/PhysRevLett.132.066004},

year  = {2024},

date = {2024-01-01},

journal = {Physical Review Letters},

volume = {132},

number = {6},

abstract = {We have investigated the 3d orbital excitations in CaCuO2 (CCO), Nd2CuO4 (NCO), and La2CuO4 (LCO) using high-resolution resonant inelastic x-ray scattering. In LCO they behave as well-localized excitations, similarly to several other cuprates. On the contrary, in CCO and NCO the dxy orbital clearly disperses, pointing to a collective character of this excitation (orbiton) in compounds without apical oxygen. We ascribe the origin of the dispersion as stemming from a substantial next-nearest-neighbor (NNN) orbital superexchange. Such an exchange leads to the liberation of the orbiton from its coupling to magnons, which is associated with the orbiton hopping between nearest neighbor copper sites. Finally, we show that the exceptionally large NNN orbital superexchange can be traced back to the absence of apical oxygens suppressing the charge transfer energy. © 2024 American Physical Society.},

note = {Cited by: 0; All Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Magnaterra2023,

title = {RIXS interferometry and the role of disorder in the quantum magnet Ba3 Ti3-x Irx O9},

author = {M. Magnaterra and M. Moretti Sala and G. Monaco and P. Becker and M. Hermanns and P. Warzanowski and T. Lorenz and D. I. Khomskii and P. H. M. Van Loosdrecht and J. Van Den Brink and M. Grüninger},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85151382686&doi=10.1103%2fPhysRevResearch.5.013167&partnerID=40&md5=fc3c9f2ca07b6bb6f27c6c0fb0dd29a2},

doi = {10.1103/PhysRevResearch.5.013167},

year  = {2023},

date = {2023-01-01},

journal = {Physical Review Research},

volume = {5},

number = {1},

abstract = {Motivated by several claims of spin-orbit-driven spin-liquid physics in hexagonal Ba3Ti3-xIrxO9 hosting Ir2O9 dimers, we report on resonant inelastic x-ray scattering (RIXS) at the Ir L3 edge for different x. We demonstrate that magnetism in Ba3Ti3-xIrxO9 is governed by an unconventional realization of strong disorder, where cation disorder affects the character of the local moments. RIXS interferometry, studying the RIXS intensity over a broad range of transferred momentum q, is ideally suited to assign different excitations to different Ir sites. We find pronounced Ir-Ti site mixing. Both ions are distributed over two crystallographically inequivalent sites, giving rise to a coexistence of quasimolecular singlet states on Ir2O9 dimers and spin-orbit-entangled j=1/2 moments of 5d5Ir4+ ions. RIXS reveals different kinds of strong magnetic couplings for different bonding geometries, highlighting the role of cation disorder for the suppression of long-range magnetic order in this family of compounds. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.},

note = {Cited by: 0; All Open Access, Gold Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Arpaia2023,

title = {Signature of quantum criticality in cuprates by charge density fluctuations},

author = {Riccardo Arpaia and Leonardo Martinelli and Marco Moretti Sala and Sergio Caprara and Abhishek Nag and Nicholas B. Brookes and Pietro Camisa and Qizhi Li and Qiang Gao and Xingjiang Zhou and Mirian Garcia-Fernandez and Ke-Jin Zhou and Enrico Schierle and Thilo Bauch and Ying Ying Peng and Carlo Di Castro and Marco Grilli and Floriana Lombardi and Lucio Braicovich and Giacomo Ghiringhelli},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85176135995&doi=10.1038%2fs41467-023-42961-5&partnerID=40&md5=c4fc5c4a9a28017a98437bb4d2a9b4f9},

doi = {10.1038/s41467-023-42961-5},

year  = {2023},

date = {2023-01-01},

journal = {Nature Communications},

volume = {14},

number = {1},

abstract = {The universality of the strange metal phase in many quantum materials is often attributed to the presence of a quantum critical point (QCP), a zero-temperature phase transition ruled by quantum fluctuations. In cuprates, where superconductivity hinders direct QCP observation, indirect evidence comes from the identification of fluctuations compatible with the strange metal phase. Here we show that the recently discovered charge density fluctuations (CDF) possess the right properties to be associated to a quantum phase transition. Using resonant x-ray scattering, we studied the CDF in two families of cuprate superconductors across a wide doping range (up to p = 0.22). At p* ≈ 0.19, the putative QCP, the CDF intensity peaks, and the characteristic energy Δ is minimum, marking a wedge-shaped region in the phase diagram indicative of a quantum critical behavior, albeit with anomalies. These findings strengthen the role of charge order in explaining strange metal phenomenology and provide insights into high-temperature superconductivity. © 2023, The Author(s).},

note = {All Open Access, Gold Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Warzanowski2023,

title = {Electronic excitations in 5d4 J=0 Os4+ halides studied by resonant inelastic x-ray scattering and optical spectroscopy},

author = {P. Warzanowski and M. Magnaterra and P. Stein and G. Schlicht and Q. Faure and Ch. J. Sahle and T. Lorenz and P. Becker and L. Bohatý and M. Moretti Sala and G. Monaco and P. H. M. Van Loosdrecht and M. Grüninger},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85173560315&doi=10.1103%2fPhysRevB.108.125120&partnerID=40&md5=fc8ddfcb7cab1e4064b34e1808b61bd8},

doi = {10.1103/PhysRevB.108.125120},

year  = {2023},

date = {2023-01-01},

journal = {Physical Review B},

volume = {108},

number = {12},

abstract = {We demonstrate that the cubic antifluorite-type halides K2OsCl6,K2OsBr6, and Rb2OsBr6 are excellent realizations of nonmagnetic J=0 compounds. The magnetic susceptibility shows the corresponding Van Vleck type of behavior and no sign of defects. We investigate the electronic excitations with two complementary techniques, resonant inelastic x-ray scattering and optical spectroscopy. This powerful combination allows us to thoroughly study, e.g., on-site intra-t2g excitations and t2g-to-eg excitations as well as intersite excitations across the Mott gap and an exciton below the gap. In this way, we determine the electronic parameters with high accuracy, altogether yielding a comprehensive picture. In K2OsCl6, we find the spin-orbit coupling constant ζ=0.34eV, Hund's coupling JH=0.43eV, the onset of excitations across the Mott gap at Δ=2.2 eV, the cubic crystal-field splitting 10Dq=3.3 eV, and the charge-transfer energy ΔCT=4.6 eV. With JH/ζ=1.3,K2OsCl6 is in the intermediate-coupling regime. In a t2g-only Kanamori picture, the above values correspond to ζeff=0.41eV and JHeff=0.28eV, which is very close to results reported for related 5d4 iridates. In the tetragonal phase at 5 K, the noncubic crystal field causes a peak splitting of the J=1 state as small as 4 meV. Compared to K2OsCl6, the bromides K2OsBr6 and Rb2OsBr6 show about 12-14% smaller values of 10Dq and ΔCT, while the spin-orbit entangled intra-t2g excitations below 2 eV and hence ζ and JH are reduced by less than 4%. Furthermore, the Mott gap in K2OsBr6 is reduced to about 1.8 eV. © 2023 American Physical Society.},

note = {All Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Katukuri2022,

title = {Charge ordering in Ir dimers in the ground state of Formula Presented},

author = {Vamshi M. Katukuri and Xingye Lu and D. E. McNally and Marcus Dantz and Vladimir N. Strocov and M. Moretti Sala and M. H. Upton and J. Terzic and G. Cao and Oleg V. Yazyev and Thorsten Schmitt},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85124495174&doi=10.1103%2fPhysRevB.105.075114&partnerID=40&md5=0eeb5a6a9c545aa44a0ea751c677585c},

doi = {10.1103/PhysRevB.105.075114},

year  = {2022},

date = {2022-01-01},

journal = {Physical Review B},

volume = {105},

number = {7},

abstract = {It has been well established experimentally that the interplay of electronic correlations and spin-orbit interactions in Formula Presented and Formula Presented oxides results in insulating Formula Presented and Formula Presented ground states, respectively. However, in compounds where the structural dimerization of iridium ions is favorable, the direct Ir Formula Presented hybridization can be significant and takes a key role. Here, we investigate the effects of direct Ir Formula Presented hybridization in comparison with electronic correlations and spin-orbit coupling in Formula Presented, a compound with Ir dimers. Using a combination of ab initio many-body wave-function quantum chemistry calculations and resonant inelastic x-ray scattering experiments, we elucidate the electronic structure of Formula Presented. We find excellent agreement between the calculated and the measured spin-orbit excitations. Contrary to expectations, the analysis of the many-body wave function shows that the two Ir (Formula Presented and Formula Presented) ions in the Formula Presented dimer unit in this compound preserve their local Formula Presented character close to 1/2 and 0, respectively. The local point group symmetry at each of the Ir ions plays an important role, significantly limiting the direct Formula Presented hybridization. Our results emphasize that minute details in the local crystal field environment can lead to dramatic differences in the electronic states in iridates and Formula Presented oxides in general. ©2022 American Physical Society},

note = {Cited by: 1; All Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bandyopadhyay2022,

title = {Breakdown of atomic spin-orbit coupling picture in an apparently isolated pseudo-one-dimensional iridate: Sr3NaIrO6},

author = {Abhisek Bandyopadhyay and A. Chakraborty and S. Bhowal and Vinod Kumar and M. M. Sala and A. Efimenko and F. Bert and P. K. Biswas and C. Meneghini and N. Büttgen and I. Dasgupta and T. Saha Dasgupta and A. V. Mahajan and Sugata Ray},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85127842341&doi=10.1103%2fPhysRevB.105.104431&partnerID=40&md5=3bcf76d2c35ae16f394d191cd9cfe868},

doi = {10.1103/PhysRevB.105.104431},

year  = {2022},

date = {2022-01-01},

journal = {Physical Review B},

volume = {105},

number = {10},

abstract = {In the presence of strong atomic spin-orbit coupling (SOC), tending to the j-j coupling limit, 5d4 iridates are speculated to possess a nonmagnetic Jeff=0 singlet ground state from atomic consideration, which invariably gets masked due to different solid-state effects (e.g., hopping). Here, we try to probe the trueness of the atomic SOC-based proposal in an apparently one-dimensional system, Sr3NaIrO6, with well-separated Ir5+ (5d4) ions. But all the detailed experimental as well as theoretical characterizations reveal that the ground state of Sr3NaIrO6 is not nonmagnetic. However, our combined dc susceptibility χ, Na23 nuclear magnetic resonance (NMR), muon spin relaxation/rotation (μSR), and heat capacity Cp measurements clearly refute any sign of spin freezing or ordered magnetism among the Ir5+ moments due to geometrical exchange frustration, while in-depth zero-field and longitudinal field μSR investigations strongly point towards an inhomogeneous quantum spin liquid (QSL)-like ground state. In addition, the linear temperature dependence of both the NMR spin-lattice relaxation rate and the magnetic heat capacity at low temperatures suggest low-lying gapless spin excitations in the QSL phase of this material. Finally, we conclude that the effective SOC realized in d4 iridates is unlikely to offer a ground state which will be consistent with a purely atomic j-j coupling description. © 2022 American Physical Society.},

note = {Cited by: 1},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Revelli2022,

title = {Quasimolecular electronic structure of the spin-liquid candidate Ba3 InIr2 O9},

author = {A. Revelli and M. Moretti Sala and G. Monaco and M. Magnaterra and J. Attig and L. Peterlini and T. Dey and A. A. Tsirlin and P. Gegenwart and T. Fröhlich and M. Braden and C. Grams and J. Hemberger and P. Becker and P. H. M. Van Loosdrecht and D. I. Khomskii and J. Van Den Brink and M. Hermanns and M. Grüninger},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85139722065&doi=10.1103%2fPhysRevB.106.155107&partnerID=40&md5=a86d10bec34a46f712749cb513570b06},

doi = {10.1103/PhysRevB.106.155107},

year  = {2022},

date = {2022-01-01},

journal = {Physical Review B},

volume = {106},

number = {15},

abstract = {The mixed-valent iridate Ba3InIr2O9 has been discussed as a promising candidate for quantum spin-liquid behavior. The compound exhibits Ir4.5+ ions in face-sharing IrO6 octahedra forming Ir2O9 dimers with three t2g holes per dimer. Our results establish Ba3InIr2O9 as a cluster Mott insulator. Strong intradimer hopping delocalizes the three t2g holes in quasimolecular dimer states while interdimer charge fluctuations are suppressed by Coulomb repulsion. The magnetism of Ba3InIr2O9 emerges from spin-orbit entangled quasimolecular moments with yet unexplored interactions, opening up a new route to unconventional magnetic properties of 5d compounds. Using single-crystal x-ray diffraction we find the monoclinic space group C2/c already at room temperature. Dielectric spectroscopy shows insulating behavior. Resonant inelastic x-ray scattering reveals a rich excitation spectrum below 1.5 eV with a sinusoidal dynamical structure factor that unambiguously demonstrates the quasimolecular character of the electronic states. Below 0.3 eV, we observe a series of excitations. According to exact diagonalization calculations, such low-energy excitations reflect the proximity of Ba3InIr2O9 to a hopping-induced phase transition based on the condensation of a quasimolecular spin-orbit exciton. The dimer ground state roughly hosts two holes in a bonding j=12 orbital and the third hole in a bonding j=32 orbital. © 2022 American Physical Society.},

note = {Cited by: 2; All Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Vocaturo2022,

title = {Prediction of ambient-pressure superconductivity in ternary hydride PdCuHx},

author = {R. Vocaturo and C. Tresca and G. Ghiringhelli and G. Profeta},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85123766327&doi=10.1063%2f5.0076728&partnerID=40&md5=b02c54bc94873da90832e1e50feec2a6},

doi = {10.1063/5.0076728},

year  = {2022},

date = {2022-01-01},

journal = {Journal of Applied Physics},

volume = {131},

number = {3},

abstract = {We present an ab initio study of the ternary hydride PdCuH x, a parent compound of the superconducting PdH, at different hydrogen content (x = 1, 2). We investigate its structural, electronic, dynamical, and superconducting properties, demonstrating that, at low hydrogen content, the system is not a superconductor above 1 K; however, the highly hydrogenated structure is a strongly coupled superconductor. We give a solid rationale for the unusual increase of the superconducting critical temperature in hydrogenated palladium when alloyed with noble metals (Cu, Ag, and Au), as observed in Stritzker's experiments in 1972 [B. Stritzker, Z. Phys. 268, 261-264 (1974)] but never investigated with modern experimental and theoretical techniques. We highlight the important role played by H-derived phonon modes at intermediate frequencies, dynamically stabilized by anharmonic effects, as they strongly couple with states at the Fermi level. We hope that the present results will stimulate additional experimental investigations of structural, electronic, and superconducting properties of hydrogenated palladium-noble metal alloys. Indeed, if confirmed, these compounds could be considered a novel class of superconducting hydrides, showing different coupling mechanisms, which can be exploited to engineer new ambient-pressure superconductors. © 2022 Author(s).},

note = {All Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{DiCapua2022b,

title = {Orbital selective switching of ferromagnetism in an oxide quasi two-dimensional electron gas},

author = {R. Di Capua and M. Verma and M. Radovic and V. N. Strocov and C. Piamonteze and E. B. Guedes and N. C. Plumb and Yu Chen and M. D’Antuono and G. M. De Luca and E. Di Gennaro and D. Stornaiuolo and D. Preziosi and B. Jouault and F. Miletto Granozio and A. Sambri and R. Pentcheva and G. Ghiringhelli and M. Salluzzo},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85128236426&doi=10.1038%2fs41535-022-00448-4&partnerID=40&md5=2cbf5789197d9f83758af3390131f140},

doi = {10.1038/s41535-022-00448-4},

year  = {2022},

date = {2022-01-01},

journal = {npj Quantum Materials},

volume = {7},

number = {1},

abstract = {Multi-orbital physics in quasi-two-dimensional electron gases (q2DEGs) triggers intriguing phenomena not observed in bulk materials, such as unconventional superconductivity and magnetism. Here, we investigate the mechanism of orbital selective switching of the spin-polarization in the oxide q2DEG formed at the (001) interface between the LaAlO3, EuTiO3 and SrTiO3 band insulators. By using density functional theory calculations, transport, magnetic and x-ray spectroscopy measurements, we find that the filling of titanium-bands with 3dxz/3dyz orbital character in the EuTiO3 layer and at the interface with SrTiO3 induces an antiferromagnetic to ferromagnetic switching of the exchange interaction between Eu-4f7 magnetic moments. The results explain the observation of the carrier density-dependent ferromagnetic correlations and anomalous Hall effect in this q2DEG, and demonstrate how combined theoretical and experimental approaches can lead to a deeper understanding of emerging electronic phases and serve as a guide for the materials design of advanced electronic applications. © 2022, The Author(s).},

note = {All Open Access, Gold Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Martinelli2022,

title = {Fractional Spin Excitations in the Infinite-Layer Cuprate CaCuO2},

author = {Leonardo Martinelli and Davide Betto and Kurt Kummer and Riccardo Arpaia and Lucio Braicovich and Daniele Di Castro and Nicholas B. Brookes and Marco Moretti Sala and Giacomo Ghiringhelli},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85131349230&doi=10.1103%2fPhysRevX.12.021041&partnerID=40&md5=b631e4eadc5f95f148ade64b2123baf1},

doi = {10.1103/PhysRevX.12.021041},

year  = {2022},

date = {2022-01-01},

journal = {Physical Review X},

volume = {12},

number = {2},

abstract = {We use resonant inelastic x-ray scattering (RIXS) to investigate the magnetic dynamics of the infinite-layer cuprate CaCuO2. We find that close to the (1/2,0) point, the single magnon decays into a broad continuum of excitations accounting for about 80% of the total magnetic spectral weight. Polarization-resolved RIXS spectra reveal the overwhelming dominance of the spin-flip (?S=1) character of this continuum with respect to the ?S=0 multimagnon contributions. Moreover, its incident-energy dependence is identical to that of the magnon, supporting a common physical origin. We propose that the continuum originates from the decay of the magnon into spinon pairs, and we relate it to the exceptionally high ring exchange Jc~J1 of CaCuO2. In the infinite-layer cuprates, long-range and multisite hopping integrals are very important, and they amplify the 2D quantum magnetism effects in spite of the 3D antiferromagnetic Néel order. © 2022 authors. Published by the American Physical Society.},

note = {All Open Access, Gold Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lu2022,

title = {Identification of a characteristic doping for charge order phenomena in Bi-2212 cuprates via RIXS},

author = {Haiyu Lu and Makoto Hashimoto and Su-Di Chen and Shigeyuki Ishida and Dongjoon Song and Hiroshi Eisaki and Abhishek Nag and Mirian Garcia-Fernandez and Riccardo Arpaia and Giacomo Ghiringhelli and Lucio Braicovich and Jan Zaanen and Brian Moritz and Kurt Kummer and Nicholas B. Brookes and Ke-Jin Zhou and Zhi-Xun Shen and Thomas P. Devereaux and Wei-Sheng Lee},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85139737189&doi=10.1103%2fPhysRevB.106.155109&partnerID=40&md5=51145c42509545bf40310c330ef3ba4b},

doi = {10.1103/PhysRevB.106.155109},

year  = {2022},

date = {2022-01-01},

journal = {Physical Review B},

volume = {106},

number = {15},

abstract = {Identifying quantum critical points (QCPs) and their associated fluctuations may hold the key to unraveling the unusual electronic phenomena observed in cuprate superconductors. Recently, signatures of quantum fluctuations associated with charge order (CO) have been inferred from the anomalous enhancement of CO excitations that accompany the reduction of the CO order parameter in the superconducting state. To gain more insight into the interplay between CO and superconductivity, here we investigate the doping dependence of this phenomenon throughout the Bi-2212 cuprate phase diagram using resonant inelastic x-ray scattering (RIXS) at the Cu L3 edge. As doping increases, the CO wave vector decreases, saturating near a commensurate value of 0.25 reciprocal lattice unit beyond a characteristic doping pc, where the correlation length becomes shorter than the apparent periodicity (4a0). Such behavior is indicative of the fluctuating nature of the CO; the proliferation of CO excitations in the superconducting state also appears strongest at pc, consistent with expected behavior at a CO QCP. Intriguingly, pc appears to be near optimal doping, where the superconducting transition temperature Tc is maximal. © 2022 American Physical Society.},

note = {All Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Peng2022,

title = {Doping dependence of the electron-phonon coupling in two families of bilayer superconducting cuprates},

author = {Yingying Peng and Leonardo Martinelli and Qizhi Li and Matteo Rossi and Matteo Mitrano and Riccardo Arpaia and Marco Moretti Sala and Qiang Gao and Xuefei Guo and Gabriella Maria De Luca and Andrew Walters and Abhishek Nag and Andi Barbour and Genda Gu and Jonathan Pelliciari and Nicholas B. Brookes and Peter Abbamonte and Marco Salluzzo and Xingjiang Zhou and Ke-Jin Zhou and Valentina Bisogni and Lucio Braicovich and Steven Johnston and Giacomo Ghiringhelli},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85126433104&doi=10.1103%2fPhysRevB.105.115105&partnerID=40&md5=10c3c4955c16ad4e3a177cb0dc9721d9},

doi = {10.1103/PhysRevB.105.115105},

year  = {2022},

date = {2022-01-01},

journal = {Physical Review B},

volume = {105},

number = {11},

abstract = {While electron-phonon coupling (EPC) is crucial for Cooper pairing in conventional superconductors, its role in high-Tc superconducting cuprates is debated. Using resonant inelastic x-ray scattering at the oxygen K edge, we study the EPC in Bi2Sr2CaCu2O8+δ (Bi2212) and Nd1+xBa2-xCu3O7-δ (NBCO) at different doping levels ranging from heavily underdoped (p=0.07) to overdoped (p=0.21). We analyze the data with a localized Lang-Firsov model that allows for the coherent excitations of two phonon modes. While electronic band dispersion effects are non-negligible, we are able to perform a study of the relative values of EPC matrix elements in these cuprate families. In the case of NBCO, the choice of the excitation energy allows us to disentangle modes related to the CuO chains and the CuO2 planes. Combining the results from the two families, we find the EPC strength decreases with doping at q∥=(-0.25,0) r.l.u., but has a nonmonotonic trend as a function of doping at smaller momenta. This behavior is attributed to the screening effect of charge carriers. We also find that the phonon intensity is enhanced in the vicinity of the charge-density-wave excitations while the extracted EPC strength appears to be less sensitive to their proximity. By performing a comparative study of two cuprate families, we are able to identify general trends in the EPC for the cuprates and provide experimental input to theories invoking a synergistic role for this interaction in d-wave pairing. © 2022 American Physical Society.},

note = {All Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Krieger2022,

title = {Charge and Spin Order Dichotomy in NdNiO2 Driven by the Capping Layer},

author = {G. Krieger and L. Martinelli and S. Zeng and L. E. Chow and K. Kummer and R. Arpaia and M. Moretti Sala and N. B. Brookes and A. Ariando and N. Viart and M. Salluzzo and G. Ghiringhelli and D. Preziosi},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85134496758&doi=10.1103%2fPhysRevLett.129.027002&partnerID=40&md5=0043cb2a2e64e41f28b61e7c70ab7bc2},

doi = {10.1103/PhysRevLett.129.027002},

year  = {2022},

date = {2022-01-01},

journal = {Physical Review Letters},

volume = {129},

number = {2},

abstract = {Superconductivity in infinite-layer nickelates holds exciting analogies with that of cuprates, with similar structures and 3d-electron count. Using resonant inelastic x-ray scattering, we studied electronic and magnetic excitations and charge density correlations in Nd1-xSrxNiO2 thin films with and without an SrTiO3 capping layer. We observe dispersing magnons only in the capped samples, progressively dampened at higher doping. We detect an elastic resonant scattering peak in the uncapped x=0 compound at wave vector (∼⅓,0), remindful of the charge order signal in hole doped cuprates. The peak weakens at x=0.05 and disappears in the superconducting x=0.20 film. The role of the capping on the electronic reconstruction far from the interface remains to be understood. © 2022 American Physical Society.},

note = {All Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bachar2022,

title = {Charge-Transfer and dd excitations in AgF2},

author = {Nimrod Bachar and Kacper Koteras and Jakub Gawraczynski and Waldemar Trzciński and Józef Paszula and Riccardo Piombo and Paolo Barone and Zoran Mazej and Giacomo Ghiringhelli and Abhishek Nag and Ke-Jin Zhou and José Lorenzana and Dirk Van Der Marel and Wojciech Grochala},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85130079702&doi=10.1103%2fPhysRevResearch.4.023108&partnerID=40&md5=1a002be924f6ea498f4dff700e3f43e9},

doi = {10.1103/PhysRevResearch.4.023108},

year  = {2022},

date = {2022-01-01},

journal = {Physical Review Research},

volume = {4},

number = {2},

abstract = {Charge-transfer insulators are the parent phase of a large group of today's unconventional high-temperature superconductors. Here we study experimentally and theoretically the interband excitations of the charge-transfer insulator silver fluoride AgF2, which has been proposed as an excellent analog of oxocuprates. Optical conductivity and resonant inelastic x-ray scattering on AgF2 polycrystalline sample show a close similarity with that measured on undoped La2CuO4. While the former shows a charge-transfer gap ∼3.4 eV, larger than in the cuprate, dd excitations are nearly at the same energy in the two materials. Density functional theory and exact diagonalization cluster computations of the multiplet spectra show that AgF2 is more covalent than the cuprate, in spite of the larger fundamental gap. Furthermore, we show that AgF2 is at the verge of a charge-transfer instability. The overall resemblance of our data on AgF2 to those published previously on La2CuO4 suggests that the underlying charge-transfer insulator physics is the same, while AgF2 could also benefit from a proximity to a charge density wave phase as in BaBiO3. Therefore, our work provides a compelling support to the future use of fluoroargentates for materials' engineering of novel high-temperature superconductors. © 2022 authors.},

note = {All Open Access, Gold Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000698977800049b,

title = {Restored strange metal phase through suppression of charge density waves 

 in underdoped YBa2Cu3O7-delta},

author = {Eric Wahlberg and Riccardo Arpaia and Gotz Seibold and Matteo Rossi and Roberto Fumagalli and Edoardo Trabaldo and Nicholas B. Brookes and Lucio Braicovich and Sergio Caprara and Ulf Gran and Giacomo Ghiringhelli and Thilo Bauch and Floriana Lombardi},

doi = {10.1126/science.abc8372},

issn = {0036-8075},

year  = {2021},

date = {2021-09-01},

journal = {SCIENCE},

volume = {373},

number = {6562, SI},

pages = {1506+},

abstract = {The normal state of optimally doped cuprates is dominated by the 

 ``strange metal'' phase that shows a linear temperature (T) dependence 

 of the resistivity persisting down to the lowest T. For underdoped 

 cuprates, this behavior is lost below the pseudogap temperature T*, where charge density waves (CDWs), together with other intertwined local 

 orders, characterize the ground state. We found that the T-linear 

 resistivity of highly strained, ultrathin, underdoped YBa2Cu3O7-delta 

 films is restored when the CDW amplitude, detected by resonant inelastic 

 x-ray scattering, is suppressed. This observation suggests an intimate 

 connection between the onset of CDWs and the departure from T-linear 

 resistivity in underdoped cuprates. Our results illustrate the potential 

 of using strain control to manipulate the ground state of quantum 

 materials.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Pelliciari2021,

title = {Evolution of spin excitations from bulk to monolayer FeSe},

author = {Jonathan Pelliciari and Seher Karakuzu and Qi Song and Riccardo Arpaia and Abhishek Nag and Matteo Rossi and Jiemin Li and Tianlun Yu and Xiaoyang Chen and Rui Peng and Mirian García-Fernández and Andrew C. Walters and Qisi Wang and Jun Zhao and Giacomo Ghiringhelli and Donglai Feng and Thomas A. Maier and Ke-Jin Zhou and Steven Johnston and Riccardo Comin},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85106908570&doi=10.1038%2fs41467-021-23317-3&partnerID=40&md5=c3747bfa9576b2786e9fb132fab5cdd6},

doi = {10.1038/s41467-021-23317-3},

year  = {2021},

date = {2021-01-01},

journal = {Nature Communications},

volume = {12},

number = {1},

abstract = {In ultrathin films of FeSe grown on SrTiO3 (FeSe/STO), the superconducting transition temperature Tc is increased by almost an order of magnitude, raising questions on the pairing mechanism. As in other superconductors, antiferromagnetic spin fluctuations have been proposed to mediate SC making it essential to study the evolution of the spin dynamics of FeSe from the bulk to the ultrathin limit. Here, we investigate the spin excitations in bulk and monolayer FeSe/STO using resonant inelastic x-ray scattering (RIXS) and quantum Monte Carlo (QMC) calculations. Despite the absence of long-range magnetic order, bulk FeSe displays dispersive magnetic excitations reminiscent of other Fe-pnictides. Conversely, the spin excitations in FeSe/STO are gapped, dispersionless, and significantly hardened relative to its bulk counterpart. By comparing our RIXS results with simulations of a bilayer Hubbard model, we connect the evolution of the spin excitations to the Fermiology of the two systems revealing a remarkable reconfiguration of spin excitations in FeSe/STO, essential to understand the role of spin fluctuations in the pairing mechanism. © 2021, The Author(s).},

note = {All Open Access, Gold Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Fumagalli2021,

title = {Crystalline and magnetic structure of Ba2CuO3+δ investigated by x-ray absorption spectroscopy and resonant inelastic x-ray scattering},

author = {Roberto Fumagalli and Abhishek Nag and Stefano Agrestini and Mirian Garcia-Fernandez and Andrew C. Walters and Davide Betto and Nicholas B. Brookes and Lucio Braicovich and Ke-Jin Zhou and Giacomo Ghiringhelli and Marco Moretti Sala},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85099701000&doi=10.1016%2fj.physc.2020.1353810&partnerID=40&md5=357e62ea98a1653bc40b3e7e383da545},

doi = {10.1016/j.physc.2020.1353810},

year  = {2021},

date = {2021-01-01},

journal = {Physica C: Superconductivity and its Applications},

volume = {581},

abstract = {Motivated by the recent synthesis of Ba2CuO3+δ (BCO), a high temperature superconducting cuprate with putative d3z ground state symmetry, we investigated its electronic structure by means of Cu L3 x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS) at the Cu L3 edge on a polycrystalline sample. We show that the XAS profile of BCO is characterised by two peaks associated to inequivalent Cu sites, and that its RIXS response features a single, sharp peak associated to crystal-field excitations. We argue that these observations are only partially compatible with the previously proposed crystal structure of BCO. Based on our spectroscopic results and on previously published powder diffraction measurements, we propose a crystalline structure characterized by two inequivalent Cu sites located at alternated planes along the c axis: nominally trivalent Cu(1) belonging to very short Cu-O chains, and divalent Cu(2) in the oxygen deficient CuO1.5 planes. We also analyze the low-energy region of the RIXS spectra to estimate the magnitude of the magnetic interactions in BCO and find that in-plane nearest neighbor superexchange exceeds 120 meV, similarly to that of other layered cuprates. Although these results do not support the pure d3z ground state scenario, they hint at a significant departure from the common quasi-2D electronic structure of superconducting cuprates of pure dx symmetry. © 2020},

note = {All Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Seibold2021,

title = {Strange metal behaviour from charge density fluctuations in cuprates},

author = {Götz Seibold and Riccardo Arpaia and Ying Ying Peng and Roberto Fumagalli and Lucio Braicovich and Carlo Di Castro and Marco Grilli and Giacomo Claudio Ghiringhelli and Sergio Caprara},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85098695688&doi=10.1038%2fs42005-020-00505-z&partnerID=40&md5=4dd84055904a0bbd1174da38a3504194},

doi = {10.1038/s42005-020-00505-z},

year  = {2021},

date = {2021-01-01},

journal = {Communications Physics},

volume = {4},

number = {1},

abstract = {Besides the mechanism responsible for high critical temperature superconductivity, the grand unresolved issue of the cuprates is the occurrence of a strange metallic state above the so-called pseudogap temperature T*. Even though such state has been successfully described within a phenomenological scheme, the so-called Marginal Fermi-Liquid theory, a microscopic explanation is still missing. However, recent resonant X-ray scattering experiments identified a new class of charge density fluctuations characterized by low characteristic energies and short correlation lengths, which are related to the well-known charge density waves. These fluctuations are present over a wide region of the temperature-vs-doping phase diagram and extend well above T*. Here we investigate the consequences of charge density fluctuations on the electron and transport properties and find that they can explain the strange metal phenomenology. Therefore, charge density fluctuations are likely the long-sought microscopic mechanism underlying the peculiarities of the metallic state of cuprates. © 2021, The Author(s).},

note = {All Open Access, Gold Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Betto2021,

title = {Multiple-magnon excitations shape the spin spectrum of cuprate parent compounds},

author = {Davide Betto and Roberto Fumagalli and Leonardo Martinelli and Matteo Rossi and Riccardo Piombo and Kazuyoshi Yoshimi and Daniele Di Castro and Emiliano Di Gennaro and Alessia Sambri and Doug Bonn and George A. Sawatzky and Lucio Braicovich and Nicholas B. Brookes and José Lorenzana and Giacomo Ghiringhelli},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85105533045&doi=10.1103%2fPhysRevB.103.L140409&partnerID=40&md5=573c83d35ea17fb2828122b8d2aec139},

doi = {10.1103/PhysRevB.103.L140409},

year  = {2021},

date = {2021-01-01},

journal = {Physical Review B},

volume = {103},

number = {14},

abstract = {Thanks to high resolution and polarization analysis, resonant inelastic x-ray scattering (RIXS) magnetic spectra of La2CuO4, Sr2CuO2Cl2 and CaCuO2 reveal a rich set of properties of the spin-1/2 antiferromagnetic square lattice of cuprates. The leading single-magnon peak energy dispersion is in excellent agreement with the corresponding inelastic neutron scattering measurements. However, the RIXS data unveil an asymmetric line shape possibly due to odd higher order terms. Moreover, a sharp bimagnon feature emerges from the continuum at (1/2,0), coincident in energy with the bimagnon peak detected in optical spectroscopy. These findings show that the inherently complex spin spectra of cuprates, an exquisite manifestation of quantum magnetism, can be effectively explored by exploiting the richness of RIXS cross sections. © 2021 American Physical Society.},

note = {All Open Access, Green Open Access},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Distefano2021,

title = {Bias polarization characterization of Al/CdTe/Pt Schottky X-ray detector for industrial applications},

author = {P. Distefano and M. Maraschi and D. Macera and B. Garavelli and M. Sammartini and G. Bertuccio and G. Ghiringhelli},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85117589654&doi=10.1016%2fj.nima.2021.165902&partnerID=40&md5=718cc301d113ba5e9d4ff3977df47ce8},

doi = {10.1016/j.nima.2021.165902},

year  = {2021},

date = {2021-01-01},

journal = {Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment},

volume = {1019},

abstract = {Al/CdTe/Pt Schottky diodes are commonly used as X-ray and γ-ray detectors thanks to their high absorption coefficients and room temperature working conditions. One known drawback is the bias induced polarization, which downgrades the spectroscopic performances by progressively decreasing the charge collection efficiency. In the frame of charge accumulation model (CAM), the bias induced polarization is explained with Cd vacancies that create a deep acceptor level inside the gap: when a reverse voltage is applied, this level is thermally populated deforming the electric field inside the detector. We measured the reverse current transient at different temperatures and interpreted the experimental results with the CAM. In particular, we investigated the Schottky barrier height, its relation to the electric field at the anode, the ratio between deep trap concentration and de-trapping time and the energy of the deep acceptor level. We estimate an energy of 0.59eV above the valence band edge for the acceptor level. We propose a variation to the CAM that takes into account two deep acceptor levels, instead of only one, this allows to improve the fittings of the time dependence of the electric field at the anode. © 2021 Elsevier B.V.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000592432200004,

title = {Two-dimensional electron systems in perovskite oxide heterostructures: 

 Role of the polarity-induced substitutional defects},

author = {Shih-Chieh Lin and Cheng-Tai Kuo and Yu-Cheng Shao and Yi-De Chuang and Jaap Geessinck and Mark Huijben and Jean-Pascal Rueff and Ismael L. Graff and Giuseppina Conti and Yingying Peng and Aaron Bostwick and Eric Gullikson and Eric Gullikson and Slavomir Nemsak and Arturas Vailionis and Nicolas Gauquelin and Johan Verbeeck and Giacomo Ghiringhelli and Claus M. Schneider and Charles S. Fadley},

doi = {10.1103/PhysRevMaterials.4.115002},

issn = {2475-9953},

year  = {2020},

date = {2020-11-01},

journal = {PHYSICAL REVIEW MATERIALS},

volume = {4},

number = {11},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {The discovery of a two-dimensional electron system (2DES) at the 

 interfaces of perovskite oxides such as LaAlO3 and SrTiO3 has motivated 

 enormous efforts in engineering interfacial functionalities with this 

 type of oxide heterostructures. However, the fundamental origins of the 

 2DES are still not understood, e.g., the microscopic mechanisms of 

 coexisting interface conductivity and magnetism. Here we report a 

 comprehensive spectroscopic investigation on the depth profile of 

 2DES-relevant Ti 3d interface carriers using depthand element-specific 

 techniques like standing-wave excited photoemission and resonant 

 inelastic scattering. We found that one type of Ti 3d interface 

 carriers, which give rise to the 2DES are located within three unit 

 cells from the n-type interface in the SrTiO3 layer. Unexpectedly, 

 another type of interface carriers, which are polarity-induced Ti-on-Al 

 antisite defects, reside in the first three unit cells of the opposing 

 LaAlO3 layer (similar to 10 angstrom). Our findings provide a 

 microscopic picture of how the localized and mobile Ti 3d interface 

 carriers distribute across the interface and suggest that the 2DES and 

 2D magnetism at the LaAlO3/SrTiO3 interface have disparate explanations 

 as originating from different types of interface carriers.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000569266900009,

title = {Large Polarons as Key Quasiparticles in SrTiO3 and SrTiO3-Based 

 Heterostructures},

author = {Andrey Geondzhian and Alessia Sambri and Gabriella M. De Luca and Roberto Di Capua and Emiliano Di Gennaro and Davide Betto and Matteo Rossi and Ying Ying Peng and Roberto Fumagalli and Nicholas B. Brookes and Lucio Braicovich and Keith Gilmore and Giacomo Ghiringhelli and Marco Salluzzo},

doi = {10.1103/PhysRevLett.125.126401},

issn = {0031-9007},

year  = {2020},

date = {2020-09-01},

journal = {PHYSICAL REVIEW LETTERS},

volume = {125},

number = {12},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {Despite its simple structure and low degree of electronic correlation, 

 SrTiO3 (STO) features collective phenomena linked to charge transport 

 and, ultimately, superconductivity, that are not yet fully explained. 

 Thus, a better insight into the nature of the quasiparticles shaping the 

 electronic and conduction properties of STO is needed. We studied the 

 low-energy excitations of bulk STO and of the LaAlO3/SrTiO3 

 two-dimensional electron gas (2DEG) by Ti L-3 edge resonant inelastic 

 x-ray scattering. In all samples, we find the hallmark of polarons in 

 the form of intense dd + phonon excitations, and a decrease of the 

 LO3-mode electron-phonon coupling when going from insulating to highly 

 conducting STO single crystals and heterostructures. Both results are 

 attributed to the dynamic screening of the large polaron self-induced 

 polarization, showing that the low-temperature physics of STO and 

 STO-based 2DEGs is dominated by large polaron quasiparticles.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000566478500001,

title = {A j(eff)=1/2 pseudospinon continuum in CaIrO3},

author = {Matteo Rossi and Pietro Marabotti and Yasuyuki Hirata and Giulio Monaco and Michael Krisch and Kenya Ohgushi and Krzysztof Wohlfeld and Jeroen Brink and Marco Moretti Sala},

doi = {10.1140/epjp/s13360-020-00649-5},

issn = {2190-5444},

year  = {2020},

date = {2020-08-01},

journal = {EUROPEAN PHYSICAL JOURNAL PLUS},

volume = {135},

number = {8},

publisher = {SPRINGER HEIDELBERG},

address = {TIERGARTENSTRASSE 17, D-69121 HEIDELBERG, GERMANY},

abstract = {In so-called j(eff) = 1/2 systems, including some iridates and 

 ruthenates, the coherent superposition of t(2g) orbitals in the ground 

 state gives rise to hopping processes that strongly depend on the bond 

 geometry. Resonant inelastic X-ray scattering measurements on CaIrO3 reveal a prototypical j(eff) = 1/2 pseudospinon continuum, a hallmark of 

 one-dimensional (1D) magnetic systems despite its three-dimensional 

 crystal structure. The experimental spectra compare very well to the 

 calculated magnetic dynamical structure factor of weakly coupled 

 spin-1/2 chains. We attribute the onset of such quasi-1D magnetism to 

 the fundamental difference in the magnetic interactions between the j(eff) = 1/2 pseudospins along the corner- and edge-sharing bonds in 

 CaIrO3.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000558930700001,

title = {Coherent, high repetition rate tender x-ray free-electron laser seeded 

 by an extreme ultra-violet free-electron laser oscillator},

author = {V Petrillo and M. Opromolla and A. Bacci and F. Broggi and I Drebot and G. Ghiringhelli and E. Puppin and M. Rossetti Conti and A. R. Rossi and M. Ruijter and S. Samsam and A. Tagliaferri and G. Rossi and L. Serafini},

doi = {10.1088/1367-2630/ab9bbf},

issn = {1367-2630},

year  = {2020},

date = {2020-07-01},

journal = {NEW JOURNAL OF PHYSICS},

volume = {22},

number = {7},

publisher = {IOP PUBLISHING LTD},

address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND},

abstract = {A seeded FEL driven by a linac based on super conducting cavities, 

 generating 10(8)-10(10)coherent photons per shot at 2-5 keV with 0.2-1 

 MHz of repetition rate, can address the need of a source devoted to fine 

 analysis of matter using the linear spectroscopy technique. The seeding 

 scheme described hereafter is a multi-stage cascade upshifting the 

 radiation frequency by a factor 20-40. The x-ray range can be achieved 

 with a seed constituted by a coherent flash in the extreme ultraviolet 

 range provided by an FEL oscillator operating at 12-14 nm. The whole 

 chain of x-ray generation is described by means of start-to-end 

 three-dimensional simulations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000540268700005,

title = {Strain and electric field control of the orbital and spin order in 

 multiferroic BiMnO3},

author = {G. M. De Luca and C. A. Perroni and R. Di Capua and V Cataudella and F. Chiarella and M. Minola and N. B. Brookes and M. Salluzzo and G. Ghiringhelli},

doi = {10.1140/epjp/s13360-020-00466-w},

issn = {2190-5444},

year  = {2020},

date = {2020-06-01},

journal = {EUROPEAN PHYSICAL JOURNAL PLUS},

volume = {135},

number = {6},

publisher = {SPRINGER HEIDELBERG},

address = {TIERGARTENSTRASSE 17, D-69121 HEIDELBERG, GERMANY},

abstract = {The new frontier for spintronics is the realization of devices in which 

 the spin can be controlled by electric fields. Multiferroics, materials 

 exhibiting strong interplay between spin and orbital degrees of freedom, 

 are candidates for the realization of such a paradigm. In this work, we 

 study the magnetoelectric coupling in epitaxial BiMnO3 thin films which 

 exhibit a large saturation magnetization. By combining X-ray absorption 

 spectroscopy data and theoretical modeling, we demonstrate that BiMnO3 

 thin films have an improper magnetoelectric behavior, characterized by 

 competing antiferromagnetic and ferromagnetic correlations. As a 

 consequence, we show that in these materials the Mn-3d orbital and 

 magnetic orders can be tuned via the ferroelectric polarization, opening 

 perspectives for the realization of novel spintronic devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000603589200010,

title = {Determining the electron-phonon coupling in superconducting cuprates by 

 resonant inelastic x-ray scattering: Methods and results on 

 Nd1+xBa2-xCu3O7-delta},

author = {Lucio Braicovich and Matteo Rossi and Roberto Fumagalli and Yingying Peng and Yan Wang and Riccardo Arpaia and Davide Betto and Gabriella M. De Luca and Daniele Di Castro and Kurt Kummer and Marco Moretti Sala and Mattia Pagetti and Giuseppe Balestrino and Nicholas B. Brookes and Marco Salluzzo and Steven Johnston and Jeroen Brink and Giacomo Ghiringhelli},

doi = {10.1103/PhysRevResearch.2.023231},

year  = {2020},

date = {2020-05-01},

journal = {PHYSICAL REVIEW RESEARCH},

volume = {2},

number = {2},

abstract = {The coupling between lattice vibration quanta and valence electrons can 

 induce charge-density modulations and decisively influence the transport 

 properties of materials, e.g., leading to conventional 

 superconductivity. In high-critical-temperature superconductors, where 

 electronic correlation is the main actor, the actual role of 

 electron-phonon coupling (EPC) is being intensely debated theoretically 

 and investigated experimentally. We present an in-depth study of how the 

 EPC strength can be obtained directly from resonant inelastic x-ray 

 scattering (RIXS) data through the theoretical approach derived by Ament 

 et al. [Europhys. Lett. 95, 27008 (2011)]. The role of the model 

 parameters (e.g., phonon energy omega(0), intermediate state lifetime 

 1/Gamma, EPC matrix element M, and detuning energy Omega) is thoroughly 

 analyzed, providing general relations among them that can be used to make quantitative estimates of the dimensionless EPC g = (M/omega(0))(2) 

 without detailed microscopic modeling. We then apply these methods to 

 very high-resolution Cu L-3-edge RIXS spectra of three 

 Nd1+xBa2-xCu3O7-delta films. For the insulating antiferromagnetic parent 

 compound, the value of M as a function of the in-plane momentum transfer 

 is obtained for Cu-O bond-stretching (breathing) and bond-bending 

 (buckling) phonon branches. For the underdoped and the nearly optimally 

 doped samples, the effects of Coulomb screening and of 

 charge-density-wave correlations on M are assessed. In light of the 

 anticipated further improvements of the RIXS experimental resolution, 

 this work provides a solid framework for an exhaustive investigation of 

 the EPC in cuprates and other quantum materials.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000531732200003,

title = {Mobile orbitons in Ca2CuO3: Crucial role of Hund's exchange},

author = {R. Fumagalli and J. Heverhagen and D. Betto and R. Arpaia and M. Rossi and D. Di Castro and N. B. Brookes and M. Moretti Sala and M. Daghofer and L. Braicovich and K. Wohlfeld and G. Ghiringhelli},

doi = {10.1103/PhysRevB.101.205117},

issn = {2469-9950},

year  = {2020},

date = {2020-05-01},

journal = {PHYSICAL REVIEW B},

volume = {101},

number = {20},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {We investigate the CuL3 edge resonant inelastic x-ray scattering (RIXS) 

 spectra of a quasi-1D antiferromagnet Ca2CuO3. In addition to the 

 magnetic excitations, which are well-described by the two-spinon 

 continuum, we observe two dispersive orbital excitations, the 3d(xy) and 

 the 3d(yz) orbitons. We carry out a quantitative comparison of the RIXS 

 spectra, obtained with two distinct incident polarizations, with a 

 theoretical model. We show that any realistic spin-orbital model needs 

 to include a finite, but realistic, Hund's exchange J(H) approximate to 

 0.5 eV. Its main effect is an increase in orbiton velocities, so that 

 their theoretically calculated values match those observed 

 experimentally. Even though Hund's exchange also mediates some 

 interaction between spinon and orbiton, the picture of spin-orbit 

 separation remains intact and describes orbiton motion in this compound.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000539577200220,

title = {Structural, Electronic and Magnetic Properties of a Few Nanometer-Thick Superconducting NdBa2Cu3O7 Films},

author = {Marco Moretti Sala and Marco Salluzzo and Matteo Minola and Gabriella Maria De Luca and Greta Dellea and Vesna Srot and Yi Wang and Peter A. Aken and Matthieu Le Tacon and Bernhard Keimer and Claudia Dallera and Lucio Braicovich and Giacomo Ghiringhelli},

doi = {10.3390/nano10040817},

year  = {2020},

date = {2020-04-01},

journal = {NANOMATERIALS},

volume = {10},

number = {4},

publisher = {MDPI},

address = {ST ALBAN-ANLAGE 66, CH-4052 BASEL, SWITZERLAND},

abstract = {Epitaxial films of high critical temperature (T-c) cuprate 

 superconductors preserve their transport properties even when their 

 thickness is reduced to a few nanometers. However, when approaching the 

 single crystalline unit cell (u.c.) of thickness, T-c decreases and 

 eventually, superconductivity is lost. Strain originating from the 

 mismatch with the substrate, electronic reconstruction at the interface 

 and alteration of the chemical composition and of doping can be the 

 cause of such changes. Here, we use resonant inelastic x-ray scattering 

 at the Cu L-3 edge to study the crystal field and spin excitations of 

 NdBa2Cu3O7-x ultrathin films grown on SrTiO3, comparing 1, 2 and 80 

 u.c.-thick samples. We find that even at extremely low thicknesses, the 

 strength of the in-plane superexchange interaction is mostly preserved, 

 with just a slight decrease in the 1 u.c. with respect to the 80 

 u.c.-thick sample. We also observe spectroscopic signatures for a 

 decrease of the hole-doping at low thickness, consistent with the 

 expansion of the c-axis lattice parameter and oxygen deficiency in the 

 chains of the first unit cell, determined by high-resolution 

 transmission microscopy and x-ray diffraction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000509473800006,

title = {Spin and orbital excitations through the metal-to-insulator transition in Cd2Os2O7 probed with high-resolution resonant inelastic x-ray scattering},

author = {J. G. Vale and S. Calder and N. A. Bogdanov and C. Donnerer and Marco Moretti Sala and N. R. Davies and D. Mandrus and J. Brink and A. D. Christianson and D. F. McMorrow},

doi = {10.1103/PhysRevB.101.014441},

issn = {2469-9950},

year  = {2020},

date = {2020-01-01},

journal = {PHYSICAL REVIEW B},

volume = {101},

number = {1},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {High-resolution resonant inelastic x-ray scattering measurements (Delta E = 46 meV) have been performed on Cd2Os2O7 through the 

 metal-to-insulator transition (MIT). A magnetic excitation at 125 meV 

 evolves continuously through the MIT, in agreement with recent 

 Raman-scattering results, and provides further confirmation for an 

 all-in all-out magnetic ground state. Asymmetry of this feature is 

 likely a result of coupling between the electronic and the magnetic 

 degrees of freedom. We also observe a broad continuum of interband 

 excitations centered at 0.3 eV energy loss. This is indicative of 

 significant hybridization between Os 5d and O 2p states and the 

 concurrent itinerant nature of the system. In turn, this suggests a 

 possible breakdown of the free-ion model for Cd2Os2O7.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000496585000002,

title = {Two-pass two-way acceleration in a superconducting continuous wave linac 

 to drive low jitter x-ray free electron lasers},

author = {A. Bacci and M. Rossetti Conti and A. Bosotti and S. Cialdi and S. Di Mitri and I Drebot and L. Faillace and G. Ghiringhelli and P. Michelato and L. Monaco and M. Opromolla and R. Paparella and V Petrillo and M. Placidi and E. Puppin and A. R. Rossi and G. Rossi and D. Sertore and L. Serafini},

doi = {10.1103/PhysRevAccelBeams.22.111304},

issn = {2469-9888},

year  = {2019},

date = {2019-11-01},

journal = {PHYSICAL REVIEW ACCELERATORS AND BEAMS},

volume = {22},

number = {11},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {We present a design study of an innovative scheme to generate high rep 

 rate (MHz-class) GeV electron beams by adopting a two-pass two-way 

 acceleration in a superconducting (SC) linac operated in continuous wave 

 (CW) mode. The electron beam is accelerated twice by being reinjected in 

 opposite direction of propagation into the linac after the first 

 passage. Acceleration in opposite directions is accomplished thanks to 

 standing waves supported in rf cavities. The task of recirculating the 

 electron beam when it leaves the linac after first pass is performed by 

 a bubble-shaped arc compressor composed by a sequence of double bend 

 achromat. In this paper we address the main issues inherent to the 

 two-pass acceleration process and the preservation of the electron beam 

 quality parameters (emittance, energy spread, peak current) required to 

 operate x-ray free electron lasers (FEL) with low jitters in the 

 amplitude, spectral and temporal domain, as achieved by operating in 

 seeding and/or oscillator mode a CW FEL up to 1 MHz rep rate. Detailed 

 start-to-end simulations are shown to assess the capability of this new 

 scheme to double the electron beam energy as well as to compress the 

 electron bunch length from picoseconds down to tens of femtoseconds. The 

 advantage of such a scheme is to halve the requested linac length for 

 the same final electron beam energy, which is typically in the few GeV 

 range, as needed to drive an x-ray FEL. The AC power to supply the 

 cryogenic plant is also significantly reduced with respect to a 

 conventional single-pass SC linac for the same final energy. We are 

 reporting also x-ray FEL simulations for typical values of wavelengths 

 of interest (in the 200 eV-8 keV photon energy range) to better 

 illustrate the potentiality of this new scheme.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000484666200038,

title = {Resonant inelastic X-ray scattering of magnetic excitations under 

 pressure},

author = {Matteo Rossi and Christian Henriquet and Jeroen Jacobs and Christian Donnerer and Stefano Boseggia and Ali Al-Zein and Roberto Fumagalli and Yi Yao and James G. Vale and Emily C. Hunter and Robin S. Perry and Innokenty Kantor and Gaston Garbarino and Wilson Crichton and Giulio Monaco and Desmond F. McMorrow and Michael Krisch and Marco Moretti Sala},

doi = {10.1107/S1600577519008877},

issn = {0909-0495},

year  = {2019},

date = {2019-09-01},

journal = {JOURNAL OF SYNCHROTRON RADIATION},

volume = {26},

number = {5},

pages = {1725-1732},

publisher = {INT UNION CRYSTALLOGRAPHY},

address = {2 ABBEY SQ, CHESTER, CH1 2HU, ENGLAND},

abstract = {Resonant inelastic X-ray scattering (RIXS) is an extremely valuable tool 

 for the study of elementary, including magnetic, excitations in matter. 

 The latest developments of this technique have mostly been aimed at 

 improving the energy resolution and performing polarization analysis of 

 the scattered radiation, with a great impact on the interpretation and 

 applicability of RIXS. Instead, this article focuses on the sample 

 environment and presents a setup for high-pressure low-temperature RIXS 

 measurements of low-energy excitations. The feasibility of these 

 experiments is proved by probing the magnetic excitations of the bilayer 

 iridate Sr3Ir2O7 at pressures up to 12GPa.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000485200600001,

title = {Formation of Incommensurate Charge Density Waves in Cuprates},

author = {H. Miao and R. Fumagalli and M. Rossi and J. Lorenzana and G. Seibold and F. Yakhou-Harris and K. Kummer and N. B. Brookes and G. D. Gu and L. Braicovich and G. Ghiringhelli and M. P. M. Dean},

doi = {10.1103/PhysRevX.9.031042},

issn = {2160-3308},

year  = {2019},

date = {2019-09-01},

journal = {PHYSICAL REVIEW X},

volume = {9},

number = {3},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {Although charge density waves (CDWs) are omnipresent in cuprate 

 high-temperature superconductors, they occur at significantly different 

 wave vectors, confounding efforts to understand their formation 

 mechanism. Here, we use resonant inelastic x-ray scattering to 

 investigate the doping- and temperature-dependent CDW evolution in La2-xBaxCuO4 (x = 0.115-0.155). We discover that the CDW develops in two 

 stages with decreasing temperature. A precursor CDW with a 

 quasicommensurate wave vector emerges first at high temperature. This 

 doping-independent precursor CDW correlation originates from the CDW 

 phase mode coupled with a phonon and ``seeds'' the low-temperature CDW 

 with a strongly doping-dependent wave vector. Our observation reveals 

 the precursor CDW and its phase mode as the building blocks of the 

 highly intertwined electronic ground state in the cuprates.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000462338300085,

title = {Resonant Inelastic Soft X-ray Scattering Study of Co-Doped Maghemite 

 Nanoparticles},

author = {Francesco Borgatti and Francesco Pineider and Marco Moretti Sala and Matteo Minola and Elvira Fantechi and Giacomo Ghiringhelli and Nicholas B. Brookes and Lucio Braicovich and Claudio Sangregorio},

doi = {10.1166/jnn.2019.16795},

issn = {1533-4880},

year  = {2019},

date = {2019-08-01},

journal = {JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY},

volume = {19},

number = {8},

pages = {4980-4986},

publisher = {AMER SCIENTIFIC PUBLISHERS},

address = {26650 THE OLD RD, STE 208, VALENCIA, CA 91381-0751 USA},

abstract = {Cobalt ferrite nanoparticles have been attracting considerable interest 

 in the recent years because of the large number of potential 

 applications, including magnetic storage, magnetic fluid hyperthermia 

 and as contrast agents for magnetic resonance imaging. Physical 

 properties of this class of materials depend critically on a number of 

 parameters, including crystallinity, stoichiometry and cation 

 distribution. In this work we have performed a Resonant Inelastic soft 

 X-ray Scattering (RIXS) study on a series of 5 nm cobalt-doped maghemite 

 nanoparticles to obtain direct quantitative information on cation 

 distribution as a function of cobalt doping. We found that the 

 distribution of divalent cobalt is stable in the investigated doping 

 range and slightly different from that of bulk, stoichiometric cobalt 

 ferrite. These results confirm that cobalt doping can be used to finely 

 tune the magnetic properties of nanostructured ferrites without 

 modifying their structural integrity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000470063800033,

title = {Enhanced spatial resolution of commercial soft X-ray CCD detectors by 

 single-photon centroid reconstruction: Technical Note},

author = {A. Amorese and C. Langini and G. Dellea and K. Kummer and N. B. Brookes and L. Braicovich and G. Ghiringhelli},

doi = {10.1016/j.nima.2019.02.044},

issn = {0168-9002},

year  = {2019},

date = {2019-08-01},

journal = {NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION 

 A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT},

volume = {935},

pages = {227-231},

publisher = {ELSEVIER SCIENCE BV},

address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS},

abstract = {The spatial resolution achieved in many back-illuminated Charge Coupled 

 Device (CCD) x-ray detectors is limited by the charge spread over the 

 pixels. For low flux measurements charge-cloud centroiding methods can 

 achieve sub-pixel spatial resolution. Experimental measurements have 

 been performed testing the performance of commercially available soft 

 x-ray CCD detectors (Amorese et al., 2019). In this technical note the 

 centroiding methods used and the numerical tests performed to test the 

 method are described. Finally, more advanced corrective algorithms are 

 discussed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000470063800032,

title = {Enhanced spatial resolution of commercial soft X-ray CCD detectors by 

 single-photon centroid reconstruction},

author = {A. Amorese and C. Langini and G. Dellea and K. Kummer and N. B. Brookes and L. Braicovich and G. Ghiringhelli},

doi = {10.1016/j.nima.2019.03.010},

issn = {0168-9002},

year  = {2019},

date = {2019-08-01},

journal = {NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION 

 A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT},

volume = {935},

pages = {222-226},

publisher = {ELSEVIER SCIENCE BV},

address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS},

abstract = {In many back-illuminated Charge Coupled Device (CCD) detectors the 

 electrons liberated by the absorption of one X-ray photon quickly spread 

 and generate charge-spots larger than the pixel dimensions. Such 

 detectors are considered here. In the soft X-ray range this phenomenon 

 drastically limits the effective spatial resolution to approximately 25 

 mu m, irrespective of the pixel's lateral size. For very low flux the 

 charge-cloud centroid determination can be used, on each individual 

 spot, to estimate the actual photon impact position with sub-pixel 

 precision. The readout noise and speed, together with the charge and 

 spatial undersampling, are the main factors limiting the accuracy of 

 this procedure in commercial devices. We have experimentally measured a 

 position uncertainty better than 7 mu m and 10 mu m for 13.5 mu m and 

 20.0 mu m pixel sizes respectively, around 1 keV photon energy using 

 centroiding algorithms. This study was motivated by the need of high 

 resolution detectors in resonant inelastic (soft) X-ray scattering 

 (RIXS).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ISI:000482210800003,

title = {Evolution of electronic and magnetic properties in a series of iridate double perovskites Pr2-xSrxMgIrO6 (x=0, 0.5, 1.0)},

author = {Abhisek Bandyopadhyay and Ilaria Carlomagno and Laura Simonelli and M. Sala and A. Efimenko and Carlo Meneghini and Sugata Ray},

doi = {10.1103/PhysRevB.100.064416},

issn = {2469-9950},

year  = {2019},

date = {2019-08-01},

journal = {PHYSICAL REVIEW B},

volume = {100},

number = {6},

publisher = {AMER PHYSICAL SOC},

address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},

abstract = {Spin-orbit coupling (SOC) plays a crucial role in magnetic and 

 electronic properties of 5d iridates. In this paper we have 

 experimentally investigated the structural and physical properties of a series of Ir-based double perovskite compounds Pr2-xSrxMgIrO6(x = 0, 

 0.5, 1; hereafter abbreviated as PMIO, PSMIO1505, and PSMIO). 

 Interestingly, these compounds have recently been proposed to undergo a transition from the spin-orbit-coupled Mott insulating phase at x = 0 to 

 the elusive half-metallic antiferromagnetic (HMAFM) state with Sr doping at x = 1. However, our detailed magnetic and electrical measurements 

 refute any kind of HMAFM possibility in either of the doped samples. In 

 addition, we establish that within these Pr2-xSrxMgIrO6 double 

 perovskites, changes in Ir-oxidation states (4+ for PMIO to 5+ for PSMIO 

 via mixed 4+/5+ for PSMIO1505) lead to markedly different magnetic 

 behaviors. While SOC on Ir is at the root of the observed insulating 

 behaviors for all three samples, the correlated magnetic properties of 

 these three compounds develop entirely due to the contribution from 

 local Ir moments. Additionally, the magnetic Pr3+ (4f(2)) ions, instead 

 of showing any kind of ordering, only contribute to the total 

 paramagnetic moment. It is seen that the PrSrMgIrO6 sample does not 

 order down to 2 K despite antiferromagnetic interactions. But, the d(5) 

 iridate Pr2MgIrO6 shows a sharp antiferromagnetic (AFM) transition at 

 around 14 K, and in the mixed valent Pr1.5Sr0.5MgIrO6 sample the AFM 

 transition is shifted to a much lower temperature (similar to 6 K) due 

 to weakening of the AFM exchange.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}