Unconventional spin-phonon coupling in 4d and 5d transition metal oxides

Invited

Abstract

The spin-phonon (SP) coupling has long been a central theme in condensed matter physics. To date, most of these phenomena have been understood by considering the Heisenberg interaction between spins. However, recent studies on 4d/5d transition metal oxides (TMOs) have revealed that strong spin-orbit coupling (SOC) plays the crucial role in their magnetism. Since the orbitals are generically coupled to the lattice, the strong SOC present in 4d/5d orbitals creates strong and inevitable interactions between spin and lattice.
Using optical spectroscopy, we carried out comparative studies on the 5d TMOs. From infrared (IR) phonon spectra, we discovered unconventional SP coupling in Cd2Os2O7 and Y2Ir2O7. For Cd2Os2O7, we observed large phonon frequency shifts below TN. This is due to the SP coupling arising from single-ion anisotropy [1,2]. We also identified frequency shifts of Y2Ir2O7 near TN. However, in this case, the Dzyaloshinskii-Moriya interaction plays a crucial role in the phonon renormalization [3]. Using near-IR pump-probe technique, we investigated coherent phonon oscillations of 4d TMO. Recently, Ca2RuO4 has been of particular interest due to its exotic magnetic ground state driven by strong SOC. We observed that a coherent Ag phonon oscillation changes abruptly its amplitude and phase as the spin order develops. Density functional theory calculations revealed that the structural deformation by the magnetic order can induce such variations in coherent phonons, which we suggest as a unique signature of SP coupling [4].
Our comprehensive studies on unconventional SP coupling may lead to scientific advancement in 4d/5d TMOs, and possibly endow opening new research fields come across.

[1] C. H. Sohn et al., Phys. Rev. Lett. 118, 117201 (2017).
[2] T. M. H. Nguyen et al., Nat. Commun. 8, 251 (2017).
[3] J. Son et al., in preparation.
[4] M.-C. Lee et al., Phys. Rev. B 98, 161115 (2018).

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Presenters

  • Tae Won Noh

    Department of Physics and Astronomy, Seoul National University, Seoul National University

Authors

  • Tae Won Noh

    Department of Physics and Astronomy, Seoul National University, Seoul National University

  • Changhee Sohn

    Materials Science and Technology Division, Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge National Lab, Materials Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge National Laboratory

  • Jaeseok Son

    Department of Physics and Astronomy, Seoul National University

  • Min-Cheol Lee

    Department of Physics and Astronomy, Seoul National University

  • Choong Kim

    Department of Physics and Astronomy, Seoul National University

  • Zenji Hiroi

    Institute for Solid State Physics, University of Tokyo, ISSP, University of Tokyo

  • Je-Guen Park

    Department of Physics and Astronomy, Seoul National University, Center for Correlated Electron Systems, Institute for Basic Science & Seoul National Univeristy, 2 Center for Correlated Electron Systems, institute for Basic Science; and 3 Department of Physics and Astronomy ,Seoul National University, Seoul, South Korea, Department of Physics and Astronomy, Seoul National University (SNU), Seoul National University, Department of Physics & Astronomy, Seoul National University, Seoul, Korea, Center for Correlated Electron Systems, Institute for Basic Science (IBS), Korea

  • Yoshiteru Maeno

    Department of Physics, Kyoto University, Dept. of Physics, Kyoto University, Department of Physics, Graduate School of Science, Kyoto University, Kyoto, Japan, Kyoto University, Department of Physics, Graduate School of Science, Kyoto University, Department of Physics, Kyoto University, Kyoto 606-8502, Japan, Department of Physics, Kyoto University, Japan