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Oral: Anisotropic phonon softening and broadening in strongly electron-phonon coupled Ta<sub>2</sub>NiSe<sub>5</sub>

ORAL

Abstract

The search for intrinsic excitonic insulator has long been confounded by possible electronic coupling to phonons in bulk materials. One way to provide clarity is to directly inspect the optical and acoustic phonons' response with and without low-energy electrons to couple to. Here, we report that the quasi-one-dimensional (quasi-1D) excitonic insulator candidate Ta2NiSe5, which hosts simultaneous second order structural and electronic transitions at 329 K, shows extremely anisotropic phonon broadening and softening during the transition. In contrast, such a response is completely absent in the isostructural Ta2NiS5, which is both transition-free and fully electronically gapped. We estimate the zero-momentum electron-phonon coupling vertex for the 2-THz B2g shear phonon to be ~100 meV in Ta2NiSe5 through a joint analysis of the electron density of states and phonon linewidth. Our results suggest the phase transition in the material family Ta2Ni(Se,S)5 is closely associated with the lattice coupling to low-energy single-electron excitations rather than excitons.

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Presenters

  • Zhibo Kang

    Yale University

Authors

  • Zhibo Kang

    Yale University

  • Xiang Chen

    Lawrence Berkeley National Laboratory

  • Weichen Tang

    University of California, Berkeley, Department of Physics, University of California at Berkeley and Materials Sciences Division, Lawrence Berkeley National Laboratory

  • Cheng Chen

    University of Oxford

  • Burak Gurlek

    Max Planck Institute for the Structure & Dynamics of Matter

  • Ahmet Alatas

    Argonne National Laboratory

  • Jacob Ruff

    Cornell University

  • Ayman H Said

    Argonne National Laboratory, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA

  • Makoto Hashimoto

    SLAC National Accelerator Laboratory

  • Donghui Lu

    SLAC National Accelerator Laboratory

  • Simone Latini

    Technical University of Denmark

  • Robert J Birgeneau

    University of California, Berkeley

  • Yulin Chen

    University of Oxford

  • Steven G Louie

    University of California, Berkeley, University of California, Berkeley and Lawrence Berkeley National Lab, University of California, Berkeley and Lawrence Berkeley National Laboratory, Department of Physics, University of California at Berkeley and Materials Sciences Division, Lawrence Berkeley National Laboratory, Department of Physics, University of California at Berkeley, Berkeley, CA, USA and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

  • Yu He

    Yale University