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