The spontaneous symmetry breaking in Ta<sub>2</sub>NiSe<sub>5</sub> is structural in nature

 · Invited

Abstract

The excitonic insulator is an electronically driven phase of matter that emerges upon the spontaneous formation and Bose condensation of excitons. Detecting this exotic order in candidate materials is a subject of paramount importance, as the size of the excitonic gap in the band structure establishes the potential of this collective state for superfluid energy transport. However, the identification of this phase in real solids is hindered by the coexistence of a structural order parameter with the same symmetry as the excitonic order. Only a few materials are currently believed to host a dominant excitonic phase, Ta2NiSe5 being the most promising. Here, we test this scenario by using an ultrashort laser pulse to quench the broken-symmetry phase of this transition metal chalcogenide. Tracking the dynamics of the material's electronic and crystal structure after light excitation reveals surprising spectroscopic fingerprints that are only compatible with a primary order parameter of phononic nature. We rationalize our findings through state-of-the-art calculations, confirming that the structural order accounts for most of the electronic gap opening. Our findings conclusively rule out any substantial excitonic character in this instability of Ta2NiSe5.

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Presenters

  • Nuh Gedik

    • Massachusetts Institute of Technology MIT
    • Massachusetts Institute of Technology

Authors

  • Edoardo Baldini

    • Massachusetts Institute of Technology MIT

  • Alfred Zong

    • University of California, Berkeley
    • Massachusetts Institute of Technology MIT
    • Massachusetts Institute of Technology

  • Dongsung Choi

    • Massachusetts Institute of Technology MIT

  • Changmin Lee

    • Lawrence Berkeley National Laboratory
    • Massachusetts Institute of Technology MIT

  • Marios H Michael

    • Harvard University

  • Lukas Windgaetter

    • Max Planck Institute for the Structure and Dynamics of Matter

  • Igor Mazin

    • Physics & Astronomy, George Mason University
    • Department of Physics and Astronomy, George Mason University
    • George Mason University
    • Physics and Astronomy, George Mason University
    • Physics, George Mason University
    • Department of Physics and Astronomy,, George Mason University
    • Department of Physics and Astronomy and Quantum Science and Engineering Center, George Mason University – Fairfax, VA, USA

  • Simone Latini

    • Max Planck Institute for the Structure and Dynamics of Matter

  • Doron Azoury

    • Massachusetts Institute of Technology MIT

  • Baiqing Lyu

    • Massachusetts Institute of Technology MIT

  • Anshul Kogar

    • Massachusetts Institute of Technology MIT
    • Massachusetts Institute of Technology

  • Yao Wang

    • Harvard University
    • Clemson University

  • Yangfan Lu

    • University of Tokyo

  • Tomohiro Takayama

    • University of Tokyo (Japan)
    • Max Planck Institute for Solid State Research

  • Hidenori Takagi

    • University of Tokyo (Japan)
    • Max Planck Institute for Solid State Research
    • Max Planck Institute for Solid State Research, Stuttgart, Germany

  • Andrew Millis

    • Columbia University
    • Department of Physics, Columbia University
    • Flatiron Institute
    • Columbia Univ
    • Center for Computational Quantum Physics, Flatiron Institute
    • Flatiron Institute; Columbia Univ.
    • Columbia University and Center for Computational Quantum Physics, Flatiron Institute

  • Angel Rubio

    • Max Plank Institute for the Structure and Dynamics of Matter; Center for Computational Quantum Physics Flatiron Institute
    • Max Planck Institute for the Structure and Dynamics of Matter
    • Theory, Max Planck Institute for the Structure and Dynamics of Matter
    • Max Planck Inst Structure & Dynamics of Matter
    • Physics, Max Planck Institute
    • Max Planck Institute for Structure and Dynamics of Matter and Center for Free-Electron Laser Science
    • Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, 22761 Hamburg, Germany
    • Max Planck Institute for the Structure and Dynamics of Matter and Center Free-Electron Laser Science, Hamburg, Germany
    • Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany
    • MPSD Hamburg
    • Max Planck Institute
    • Max Planck Inst Structure & Dynamics of Matter; Center for Computational Quantum Physics Flatiron Institute, Simons Foundation NY, USA
    • Theory, Max Planck Inst Structure & Dynamics of Matter

  • Eugene Demler

    • Harvard University
    • Department of Physics, Harvard University

  • Nuh Gedik

    • Massachusetts Institute of Technology MIT
    • Massachusetts Institute of Technology