Quantum-Confined Electronic States Arising from the Moire Pattern of MoS2-WSe2 Heterobilayers

A two-dimensional (2D) heterobilayer system consisting of MoS2 on WSe2, deposited on epitaxial graphene, is studied by scanning tunneling microscopy and spectroscopy at temperatures of 5 and 80 K. A moire pattern is observed, arising from lattice mismatch of 3.7% between the MoS2 and WSe2. Significant energy shifts are observed in tunneling spectra observed at the maxima of the moire corrugation, as compared with spectra obtained at corrugation minima, consistent with prior work. Furthermore, at the minima of the moire corrugation, sharp peaks in the spectra at energies near the band edges are observed for spectra acquired at 5 K The peaks correspond to discrete states that are confined within the moire unit cells. Conductance mapping is employed to reveal the detailed structure of the wave functions of the states. For measurements at 80 K, the sharp peaks in the spectra are absent, and conductance maps of the band edges reveal little structure.