Making the intractable tractable: GW-BSE calculation of the nature of interlayer and intralayer moiré excitons in large-area moiré superlattices.

ORAL

Abstract

Recent experimental measurements have demonstrated signatures of novel exciton states in the moiré superlattices of transition metal dichalcogenide (TMD) bilayer heterostructures. However, the exact nature of the moiré excitons is difficult, and has yet, to be determined experimentally. An accurate description of these excitons requires a completely account of the electron and hole degrees of freedom. First-principles theoretical study of moiré excitons is strongly hindered by the O(N4) scaling of the ab initio GW-Bethe Salpeter equation method with the number of atoms (N). To overcome this challenge, we develop a Pristine Unit-cell Matrix Projection (PUMP) method, which speeds up the computation by at least six orders of magnitude. In this method, we leverage the smooth modulation of the electronic wavefunctions in the moiré superlattice to expand them in an efficient (i.e., small) basis of pristine unit-cell wavefunctions. The electron-hole interaction kernel matrix of the Bethe Salpeter equation is similarly expanded in terms of the pristine unit-cell kernel matrix elements. Using this method, we have computed the optical spectra of TMD hetero-bilayers and discovered novel interlayer and intralayer moiré excitons of dramatically different characters.

*This work was supported by the US DOE at Lawrence Berkeley National Lab under contract no. DE-AC02-05CH11231. Computational resources have been provided by NERSC, TACC and XSEDE.

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Presenters

  • Mit H Naik

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

Authors

  • Mit H Naik

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

  • Zhenglu Li

    • University of California at Berkeley, and Lawrence Berkeley National Laboratory
    • Physics Department, UC Berkeley and Lawrence Berkeley National Lab
    • Lawrence Berkeley National Laboratory
    • Lawrence Berkeley National Laboratory; University of California at Berkeley
    • University of California at Berkeley and Lawrence Berkeley National Laboratory

  • Yang-Hao Chan

    • Institute of Atomic and Molecular Sciences, Academia Sinica
    • Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei

  • Felipe H da Jornada

    • Stanford Univ
    • Stanford University

  • Steven G Louie

    • University of California at Berkeley, and Lawrence Berkeley National Laboratory
    • Physics Department, UC Berkeley and Lawrence Berkeley National Lab
    • University of California Berkeley
    • University of California, Berkeley
    • University of California at Berkeley; Lawrence Berkeley National Laboratory
    • University of California at Berkeley and Lawrence Berkeley National Laboratory
    • UC berkeley
    • University of California at Berkeley and Lawrence Berkeley National Lab
    • UC Berkeley & Lawrence Berkeley National Laboratory