by Sala, M. Moretti, Schnells, V., Boseggia, S., Simonelli, L. and Al-Zein, A., Vale, J. G., Paolasini, L., Hunter, E. C. and Perry, R. S., Prabhakaran, D., Boothroyd, A. T., Krisch, M. and Monaco, G., Ronnow, H. M., McMorrow, D. F. and Mila, F.
Abstract:
The magnetic excitation spectrum in the bilayer iridate Sr3Ir2O7 has been investigated using high-resolution resonant inelastic x-ray scattering (RIXS) performed at the iridium L-3 edge and theoretical techniques. A study of the systematic dependence of the RIXS spectrum on the orientation of the wave-vector transfer Q, with respect to the iridium-oxide bilayer, has revealed that the magnon dispersion is comprised of two branches well separated in energy and gapped across the entire Brillouin zone. Our results contrast with those of an earlier study which reported the existence of a single dominant branch. While these earlier results were interpreted as two overlapping modes within a spin-wave model of weakly coupled iridium-oxide planes, our results are more reminiscent of those expected for a system of weakly coupled dimers. In this latter approach, the lower-and higher-energy modes find a natural explanation as those corresponding to transverse and longitudinal fluctuations, respectively. We have therefore developed a bond-operator theory which describes the magnetic dispersion in Sr3Ir2O7 in terms of quantum dimer excitations. In our model, dimerization is produced by the leading Heisenberg exchange J(c), which couples iridium ions in adjacent planes of the bilayer. The Hamiltonian also includes in-plane exchange J, as well as further neighbor couplings and relevant anisotropies. The bond-operator theory provides an excellent account of the dispersion of both modes, while the measured Q dependence of the RIXS intensities is in reasonable qualitative accord with the spin-spin correlation function calculated from the theory. We discuss our results in the context of the quantum criticality of bilayer dimer systems in the presence of anisotropic interactions derived from strong spin-orbit coupling.
Reference:
Evidence of quantum dimer excitations in Sr3Ir2O7 (Sala, M. Moretti, Schnells, V., Boseggia, S., Simonelli, L. and Al-Zein, A., Vale, J. G., Paolasini, L., Hunter, E. C. and Perry, R. S., Prabhakaran, D., Boothroyd, A. T., Krisch, M. and Monaco, G., Ronnow, H. M., McMorrow, D. F. and Mila, F.), In PHYSICAL REVIEW B, AMER PHYSICAL SOC, volume 92, 2015.
Bibtex Entry:
@article{ ISI:000357485100009, Author = {Sala, M. Moretti and Schnells, V. and Boseggia, S. and Simonelli, L. and Al-Zein, A. and Vale, J. G. and Paolasini, L. and Hunter, E. C. and Perry, R. S. and Prabhakaran, D. and Boothroyd, A. T. and Krisch, M. and Monaco, G. and Ronnow, H. M. and McMorrow, D. F. and Mila, F.}, Title = {{Evidence of quantum dimer excitations in Sr3Ir2O7}}, Journal = {{PHYSICAL REVIEW B}}, Year = {{2015}}, Volume = {{92}}, Number = {{2}}, Month = {{JUL 6}}, Abstract = {{The magnetic excitation spectrum in the bilayer iridate Sr3Ir2O7 has been investigated using high-resolution resonant inelastic x-ray scattering (RIXS) performed at the iridium L-3 edge and theoretical techniques. A study of the systematic dependence of the RIXS spectrum on the orientation of the wave-vector transfer Q, with respect to the iridium-oxide bilayer, has revealed that the magnon dispersion is comprised of two branches well separated in energy and gapped across the entire Brillouin zone. Our results contrast with those of an earlier study which reported the existence of a single dominant branch. While these earlier results were interpreted as two overlapping modes within a spin-wave model of weakly coupled iridium-oxide planes, our results are more reminiscent of those expected for a system of weakly coupled dimers. In this latter approach, the lower-and higher-energy modes find a natural explanation as those corresponding to transverse and longitudinal fluctuations, respectively. We have therefore developed a bond-operator theory which describes the magnetic dispersion in Sr3Ir2O7 in terms of quantum dimer excitations. In our model, dimerization is produced by the leading Heisenberg exchange J(c), which couples iridium ions in adjacent planes of the bilayer. The Hamiltonian also includes in-plane exchange J, as well as further neighbor couplings and relevant anisotropies. The bond-operator theory provides an excellent account of the dispersion of both modes, while the measured Q dependence of the RIXS intensities is in reasonable qualitative accord with the spin-spin correlation function calculated from the theory. We discuss our results in the context of the quantum criticality of bilayer dimer systems in the presence of anisotropic interactions derived from strong spin-orbit coupling.}}, Publisher = {{AMER PHYSICAL SOC}}, Address = {{ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}}, Type = {{Article}}, Language = {{English}}, Affiliation = {{Sala, MM (Corresponding Author), European Synchrotron Radiat Facil, BP 220, F-38043 Grenoble, France. Sala, M. Moretti; Simonelli, L.; Al-Zein, A.; Paolasini, L.; Krisch, M.; Monaco, G., European Synchrotron Radiat Facil, F-38043 Grenoble, France. Schnells, V., Univ Wurzburg, Inst Theoret Phys & Astrophys, D-97074 Wurzburg, Germany. Boseggia, S.; Vale, J. G.; Perry, R. S.; McMorrow, D. F., UCL, London Ctr Nanotechnol, London WC1E 6BT, England. Boseggia, S.; Vale, J. G.; Perry, R. S.; McMorrow, D. F., UCL, Dept Phys & Astron, London WC1E 6BT, England. Boseggia, S., Diamond Light Source Ltd, Didcot OX11 0DE, Oxon, England. Simonelli, L., CELLS ALBA Synchrotron Radiat Facil, Barcelona 08290, Spain. Hunter, E. C., Ctr Sci Extreme Condit, Edinburgh EH9 3FD, Midlothian, Scotland. Prabhakaran, D.; Boothroyd, A. T., Univ Oxford, Dept Phys, Clarendon Lab, Oxford OX1 3PU, England. Monaco, G., Univ Trento, Dipartimento Fis, I-38123 Povo, TN, Italy. Ronnow, H. M., Ecole Polytech Fed Lausanne, Lab Quantum Magnetism, CH-1015 Lausanne, Switzerland. Ronnow, H. M., Univ Tokyo, Inst Solid State Phys, Neutron Sci Lab, Kashiwa, Chiba 2778581, Japan. Mila, F., Ecole Polytech Fed Lausanne, Inst Theoret Phys, CH-1015 Lausanne, Switzerland.}}, DOI = {{10.1103/PhysRevB.92.024405}}, Article-Number = {{024405}}, ISSN = {{2469-9950}}, EISSN = {{2469-9969}}, Keywords-Plus = {{SPIN GAPS; FRUSTRATION; STATES}}, Research-Areas = {{Materials Science; Physics}}, Web-of-Science-Categories = {{Materials Science, Multidisciplinary; Physics, Applied; Physics, Condensed Matter}}, ResearcherID-Numbers = {{Zein, Ali Al/F-4393-2019 Moretti, Marco/AAF-9255-2019 Krisch, Michael H/U-5662-2018 Ronnow, Henrik M/A-4953-2009 McMorrow, Desmond Francis/M-9036-2019 Simonelli, Laura/I-1963-2015 Mila, Frederic/R-4871-2019 McMorrow, Desmond/C-2655-2008 Vale, James/A-1475-2016 Monaco, Giulio/AAW-4387-2020 Sala, Marco Moretti/H-1034-2014 }}, ORCID-Numbers = {{Moretti, Marco/0000-0002-9744-9976 Krisch, Michael H/0000-0001-7423-1715 Ronnow, Henrik M/0000-0002-8832-8865 McMorrow, Desmond Francis/0000-0002-4947-7788 Mila, Frederic/0000-0003-4306-7996 McMorrow, Desmond/0000-0002-4947-7788 Vale, James/0000-0002-9148-3575 Monaco, Giulio/0000-0003-2497-6422 Sala, Marco Moretti/0000-0002-9744-9976 Giles, Emily/0000-0001-9880-1102}}, Funding-Acknowledgement = {{Swiss National Science FoundationSwiss National Science Foundation (SNSF); ERC starters grant TOPOLECTRICS {[}ERC-StG-TOPOLECTRICS-336012]; Sinergia network Mott Physics Beyond the Heisenberg Model; EPSRCEngineering & Physical Sciences Research Council (EPSRC); Engineering and Physical Sciences Research CouncilEngineering & Physical Sciences Research Council (EPSRC) {[}EP/J017124/1, EP/G007357/1, EP/J016713/1, 1268395, 1745233] Funding Source: researchfish}}, Funding-Text = {{We gratefully thank C. Henriquet and R. Verbeni for technical assistance during the experiments and B. Normand, O. Syljuaasen, and B. Dalla Piazza for insightful discussions. The work in Lausanne was supported by the Swiss National Science Foundation and its Sinergia network Mott Physics Beyond the Heisenberg Model, in London by the EPSRC, and in Wurzburg by the ERC starters grant TOPOLECTRICS under ERC-StG-TOPOLECTRICS-336012.}}, Number-of-Cited-References = {{40}}, Times-Cited = {{31}}, Usage-Count-Last-180-days = {{0}}, Usage-Count-Since-2013 = {{87}}, Journal-ISO = {{Phys. Rev. B}}, Doc-Delivery-Number = {{CM2BR}}, Unique-ID = {{ISI:000357485100009}}, OA = {{Green Published}}, DA = {{2020-12-22}}, }
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