Optical transition coupling to ferroelectric order in a 2D semiconductor

ORAL

Abstract

A ferroelectric material often exhibits a soft transverse optical (TO) phonon mode which governs it phase transition. Charge coupling to this ferroelectric soft mode may further mediate emergent physical properties, including superconductivity and defect tolerance. However, direct experimental evidence for such coupling is scarce. Here we show that a photo-launched coherent phonon couples strongly to electronic transitions across the bandgap in the van der Waals (vdW) two-dimensional (2D) ferroelectric semiconductor NbOI2. Using terahertz time-domain spectroscopy and first-principles calculations, we identify this mode as the TO phonon responsible for ferroelectric order. This exclusive coupling occurs only with above-gap electronic transition and is absent in the valence band as revealed by resonant inelastic X-ray scattering. Our findings suggest a new role of the soft TO phonon mode in electronic and optical properties of ferroelectric semiconductors.

*The Raman and coherent phonon spectroscopy experiments are supported by the US Army Research Office, grant number W911NF-23-1-0056. The THz-TDS and DFT efforts are supported by the Materials Science and Engineering Research Center (MRSEC) through NSF grant DMR-142011738. Support by the Air Force Office of Scientific Research under award number FA9550- 22-1-0389 is acknowledged for the imaging experiments. The RIXS experiments were supported by the Center on Programmable Quantum Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), under award number DE-SC0019443. This research used beamline 2-ID of NSLS-II, a US DOE Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704. C.-Y. H. is supported by the Taiwan-Columbia Fellowship funded by the Ministry of Education of Taiwan and Columbia University. M.Y.S was supported by the Gordon and Betty Moore Foundation, grant DOI 10.37807/gbmf12235.

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Publication: Coupling of Electronic Transitions to Ferroelectric Order in a 2D Semiconductor. arXiv:2410.09238

Presenters

  • Chun-Ying Huang

    • Columbia University

Authors

  • Chun-Ying Huang

    • Columbia University

  • Daniel G Chica

    • Columbia University
    • Northwestern University
    • Columbia

  • Zhihao Cui

    • Columbia University

  • Taketo Handa

    • Columbia University

  • Morgan Thinel

    • Columbia University

  • Nicholas M Olsen

    • Columbia University

  • Yufeng Liu

    • Columbia University

  • Michael E Ziebel

    • Columbia University

  • Guiying He

    • City University of New York

  • Yinming Shao

    • Pennsylvania State University
    • Columbia University, Pennsylvania State University

  • Connor A Occhialini

    • Massachusetts Institute of Technology
    • Columbia University

  • Jonathan Pelliciari

    • Brookhaven National Laboratory (BNL)
    • Brookhaven National Laboratory
    • National Synchrotron Light Source II, Brookhaven National Laboratory

  • Dmitri N Basov

    • Columbia University

  • Matthew Y Sfeir

    • The Graduate Center, City University of New York

  • Abhay Pasupathy

    • Columbia University
    • Brookhaven National Laboratory (BNL)

  • Valentina Bisogni

    • Brookhaven National Laboratory (BNL)

  • David Reichman

    • Columbia University

  • Xavier Roy

    • Columbia University

  • Xiaoyang Zhu

    • Columbia University