Temperature-driven evolution of critical points, interlayer coupling, and layer polarization in bilayer MoS2

The recently emerging two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have been a fertile ground for exploring abundant exotic physical properties. Critical points, the extrema or saddle points of electronic bands, are the cornerstone of condensed-matter physics and fundamentally determine the optical and transport phenomena of the TMDCs. However, for bilayer MoS2, a typical TMDC and the unprecedented electrically tunable venue for valleytronics, there has been a considerable controversy on its intrinsic electronic structure, especially for the conduction band-edge locations. Moreover, interlayer hopping and layer polarization in bilayer MoS2 which play vital roles in valley-spintronic applications have remained experimentally elusive. Here, we report the experimental observation of intrinsic critical points locations, interlayer hopping, layer-spin polarization, and their evolution with temperature in bilayer MoS2 by performing temperature-dependent photoluminescence. Our measurements confirm that the conduction-band minimum locates at the K-c instead of Q(c) and the energy splitting between Q(c) and K-c redshifts with a descent of temperature. Furthermore, the interlayer hopping energy for holes and temperature-dependent layer polarization are quantitatively determined. Our observations are in good harmony with density-functional theory calculations.