Low-temperature orbital ordering and dynamical frustration of spins in KCuF$_3$: Experimental

ORAL

Abstract

We present new Raman and x-ray scattering evidence for the existence of a structural phase transition at 50 K in KCuF$_3$. Phonon modes associated with the F-ions in CuF$_{6}$ octahedra soften with decreasing temperature down to 50 K, at which temperature there is a splitting of the E$_g$ phonon. Above T$_{N}$ = 40 K, diffuse resonant magnetic scattering from critical fluctuations was observed at the Cu L$_{3}$ edge. Below T$_{N}$, orbital reflections seen by 8.8 keV x-ray scattering exhibit diffuse scattering that is hysteretic with temperature, indicating glassy orbital disorder. The phase behavior of KCuF$_{3}$ above T$_{N}$ is dominated by coupled orbital/lattice fluctuations that are likely associated with dynamical rotations of the CuF$_{6}$ octahedra. A model with interactions between orbital, spin and lattice degrees of freedom explain these observations.

*Funding provided by grants from US DOE and NSF.

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Authors

  • J.C.T. Lee

    • University of Illinois at Urbana-Champaign
    • University of Illinois

  • S. Yuan

    • University of Illinois at Urbana-Champaign
    • University of Illinois

  • Siddhartha Lal

    • University of Illinois at Urbana-Champaign
    • University of Illinois
    • Dept. of Physics, University of Illinois

  • Young Il Joe

    • University of Illinois at Urbana-Champaign
    • University of Illinois

  • Yu Gan

    • University of Illinois at Urbana-Champaign
    • University of Illinois

  • Serban Smadici

    • University of Illinois at Urbana-Champaign
    • University of Illinois

  • Paul Goldbart

    • University of Illinois at Urbana-Champaign
    • Universiy of Illinois
    • University of Illinois
    • UIUC
    • Department of Physics and Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign

  • S.L. Cooper

    • University of Illinois at Urbana-Champaign
    • University of Illinois

  • P. Abbamonte

    • University of Illinois at Urbana-Champaign
    • University of Illinois

  • K.D. Finkelstein

    • Cornell High Energy Synchrotron Source, Cornell University
    • CHESS, Cornell University
    • Cornell High Energy Synchrotron Source

  • Yejun Feng

    • APS, Argonne National Lab
    • Argonne National Laboratory
    • Advanced Photon Source, Argonne National Laboratory
    • APS, Argonne National Laboratory

  • Andrivo Rusydi

    • Nanocore, Physics Dept NUS, IAP Uni Hamburg
    • National University of Singapore