Direct evidence of phonon instability driving geometric improper ferroelectricity in multiferroic YMnO3

ORAL

Abstract

In improper ferroelectrics, the anharmonic coupling between a stable zone-center polar phonon mode and unstable zone-boundary non-polar modes is theoretically proposed to drive the spontaneous polarization. However, the exact mechanism of the transition driven by the coupling between two phonon modes remains to be observed. We have performed comprehensive T-dependent phonon dispersion measurements in the archetypal improper ferroelectric, YMnO3, including the behavior across the ferroelectric transition, using inelastic neutron scattering and single-crystal x-ray diffraction. In addition, we performed both 0K and finite temperature first-principles lattice dynamics simulations, including anharmonic renormalization effects. Both experiments and simulations reveal the zone-boundary soft-mode, and its temperature dependent anharmonic coupling to the zone-center polar mode, providing direct evidence for the previously proposed mechanism of geometric improper ferroelectricity.

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Presenters

  • Dipanshu Bansal

    Materials Science and Technology, Oak Ridge National Laboratory, Duke University, Mechanical Engineering and Materials Science, Duke University

Authors

  • Dipanshu Bansal

    Materials Science and Technology, Oak Ridge National Laboratory, Duke University, Mechanical Engineering and Materials Science, Duke University

  • Jennifer Niedziela

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

  • Ryan Sinclair

    University of Tennessee

  • Vasile Garlea

    Quantum Condensed Matter Division, Oak Ridge National Laboratory, Neutron Scattering Division, Oak Ridge National Lab, Oak Ridge National Lab

  • Douglas Abernathy

    Oak Ridge National Laboratory, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge National Lab

  • Songxue Chi

    Oak Ridge National Lab, Quantum Condensed Matter Division, Oak Ridge National Laboratory, Neutron Scattering Division, Oak Ridge National Lab

  • Yang Ren

    The Advanced Photon Source, Argonne National Laboratory, Advanced Photon Source, Argonne National Laboratory, Argonne National Laboratory

  • Haidong Zhou

    Physics and Astronomy, Univ of Tennessee, Knoxville, Physics and Astronomy, University of Tennessee Knoxville, Department of Physics and Astronomy, University of Tennessee, Department of Physics and Astronomy, University of Tennessee Knoxville, Department of Physics & Astronomy, University of Tennessee, University of Tennessee, Physics and Astronomy, University of Tennessee, Physics, University of Tennessee, Univ of Tennessee, Knoxville, Physics and Astronomy, University of Tennessee, knoxville, Dept. of Physics and Astronomy, University of Tennessee

  • Olivier Delaire

    Mechanical Engineering and Materials Science, Duke University