Strong electron-phonon coupling in Ta<sub>2</sub>Ni(Se,S)<sub>5</sub> across the semimetal-semiconductor transition

ORAL

Abstract

During a band-gap tuned semimetal-to-semiconductor transition, the excitonic instability of the system, the spontaneous formation of electron-hole bound pairs via direct Coulomb attraction, often peaks when the bandgap crosses zero. However, such excitonic phase diagram can be altered in the presence of strong electron-phonon coupling. Here, via angle-resolved photoemission spectroscopy (ARPES) and high-resolution synchrotron x-ray diffraction (XRD), we report a monotonically suppressed broken-symmetry phase boundary across the semimetal-semiconductor transition in a leading excitonic insulator candidate system Ta2Ni(Se,S)5. Bolstered by first principles and model calculations, strong electron-phonon coupling is shown to substantially enhance the symmetry-breaking on the semimetal side, leading to negative electronic compressibility, pervasive lattice fluctuation, and a persistently gapped ground state. Our results not only resolve the longstanding debate about the nature of the intertwined order in Ta2NiSe5, but also lay the groundwork to a new solid-state platform for the investigation of excitonic instability amid electron-phonon solid coupling.

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Publication: C. Chen et al. arXiv:2203.06817 (2022)
C. Chen et al. in preparation

Presenters

  • Cheng Chen

    • University of Oxford

Authors

  • Cheng Chen

    • University of Oxford

  • Weichen Tang

    • University of California, Berkeley

  • Xiang Chen

    • Lawrence Berkeley National Laboratory

  • zhibo kang

    • Yale University

  • Siqi Wang

    • Yale University

  • Zhenglu Li

    • Lawrence Berkeley National Laboratory
    • University of California at Berkeley, and Lawrence Berkeley National Laboratory

  • Jacob Ruff

    • Cornell University

  • Makoto Hashimoto

    • SLAC - Natl Accelerator Lab

  • Donghui Lu

    • SLAC - Natl Accelerator Lab

  • Christopher Jozwiak

    • Lawrence Berkeley National Laboratory
    • LBNL
    • The Advanced Light Source
    • lawrence berkeley national lab
    • Lawrence Berkeley National Lab
    • Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States of America
    • Advanced Light Source, Lawrence Berkeley National Lab

  • Aaron Bostwick

    • Lawrence Berkeley National Laboratory
    • LBNL
    • The Advanced Light Source
    • lawrence berkeley national lab
    • Lawrence Berkeley National Lab
    • Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States of America
    • Advanced Light Source, Lawrence Berkeley National Lab

  • Eli Rotenberg

    • Lawrence Berkeley National Laboratory
    • Advanced Light Source, Lawrence Berkeley National Lab

  • Robert J Birgeneau

    • University of California, Berkeley

  • Yulin Chen

    • University of Oxford

  • Steven G Louie

    • University of California at Berkeley
    • University of California, Berkeley
    • University Of California, Berkeley
    • University of California at Berkeley and Lawrence Berkeley National Lab
    • University of California at Berkeley; Lawrence Berkeley National Lab
    • UC Berkeley
    • University of California at Berkeley, and Lawrence Berkeley National Laboratory
    • UC berkeley
    • Lawrence Berkeley National Laboratory
    • Physics Department, UC Berkeley and Lawrence Berkeley National Lab
    • Department of Physics, University of California at Berkeley and Materials Sciences Division, Lawrence Berkeley National Laboratory
    • LBNL & UC Berkeley

  • Yao Wang

    • Clemson University

  • Yu He

    • Yale University