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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)<br>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