Published in ACS Nano 14, 7564 (2020).

Flat Bands and Mechanical Deformation Effects in the Moiré Superlattice of MoS2-WSe2 Heterobilayers

Dacen Waters1, Yifan Nie2,3, Felix Lüpke1, Yi Pan4,5, Stefan Fölsch4, Yu-Chuan Lin6, Bhakti Jariwala6, Kehao Zhang6, Chong Wang1, Hongyan Lv1,7, Kyeongjae Cho2, Di Xiao1, Joshua A. Robinson6, and Randall M. Feenstra1
1Dept. Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA
2Dept. Materials Science and Engineering, The University of Texas at Dallas, Richardson, TX 75080, USA
3Materials Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720 USA
4Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany
5Center for Spintronics and Quantum Systems, State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an, 710049, China
6Department of Materials Science and Engineering, and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802, USA
7Key Laboratory of Materials Physics, Institute of Solid-State Physics, Chinese Academy of Sciences, Hefei, 230031, China

Abstract

It has recently been shown that quantum-confined states can appear in epitaxially grown van der Waals material heterobilayers without a rotational misalignment (θ=0°), associated with flat bands in the Brillouin zone of the moiré pattern formed due to the lattice mismatch of the two layers. Peaks in the local density of states and confinement in a MoS2/WSe2 system was qualitatively described only considering local stacking arrangements, which cause band edge energies to vary spatially. In this work, we report the presence of large in-plane strain variation across the moiré unit cell of a θ=0° MoS2/WSe2 heterobilayer, and show that inclusion of strain variation and out-of-plane displacement in density functional theory calculations greatly improves their agreement with the experimental data. We further explore the role of twist-angle by showing experimental data for a twisted MoS2/WSe2 heterobilayer structure with twist angle of θ=15°, that exhibits a moiré pattern but no confinement.

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