Structural relaxation driven exciton spectral and spatial signatures in moiré superlattices of WS<sub>2</sub>/WSe<sub>2</sub>

ORAL

Abstract

Artificial moiré superlattices of transition metal dichalcogenides formed by stacking individual monolayers have emerged as a promising platform to tune the optoelectronic properties with twist angle as an additional degree of freedom. The interplay between intralayer strain and interlayer stacking energy with varying twist angles governs the structural relaxation and the corresponding lattice symmetries. The previous studies have shown the spatial localization of moiré excitons in a twisted bilayer of WS2/WSe2 using monochromated scanning transmission electron microscope- electron energy loss spectroscopy (STEM-EELS) but with spectral resolution of 100 meV merging all fine spectral features. In this work, we image the fine structure of these excitons with a tenfold higher spectral resolution. Through simultaneous structural imaging, we correlate the spectral and spatial variation of individual moiré excitons of WSe2 and WS2, demonstrating the significance of lattice relaxation effects. We find that the lowest energy moiré exciton of WSe2 exhibits localization at AA sites only when significant lattice reconstruction occurs; otherwise, the different moiré exciton peaks delocalize across different stacking sites.

*Electron microscopy research was conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), Which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. S.S. would like to acknowledge the use of the ASU start-up funds. SS would like to acknowledge the support of the Fulton Fellowship.

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Presenters

  • Sriram Sankar

    • Arizona State University

Authors

  • Sriram Sankar

    • Arizona State University

  • Medha Dandu

    • Lawrence Berkeley National Laboratory

  • Daria Blach

    • Lawrence Berkeley national laboratory

  • Patrick Hays

    • Arizona State University

  • Takashi Taniguchi

    • National Institute for Materials Science
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science
    • Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
    • International Center for Materials Nanoarchitectonics, National Institute of Material Science, Tsukuba, Japan
    • Advanced Materials Laboratory, National Institute for Materials Science

  • Kenji Watanabe

    • National Institute for Materials Science
    • NIMS
    • Research Center for Functional Materials, National Institute for Materials Science
    • Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
    • Research Center for Functional Materials, National Institute of Material Science, Tsukuba, Japan
    • National Institute of Materials Science
    • Advanced Materials Laboratory, National Institute for Materials Science

  • Felipe H da Jornada

    • Stanford University

  • Seth Ariel Tongay

    • Arizona State University

  • Peter Ercius

    • LBNL
    • Lawrence Berkeley National Laboratory
    • Lawrence Berkeley national laboratory

  • Jordan Hachtel

    • Oak Ridge National Laboratory

  • Mit H. Naik

    • University of California, Berkeley
    • University of Texas at Austin

  • Archana Raja

    • Lawrence Berkeley National Laboratory

  • Sandhya Susarla

    • Arizona State University