Abstract
Ultrathin films of the topological Dirac semimetal Na3Bi have recently been revealed as unusual electronic materials with field-tunable topological phases. Here we investigate the electronic and transport properties of ultrathin Na3Bi as an electrical contact to a two-dimensional (2D) metal (i.e., graphene) and 2D semiconductors (i.e., MoS2 and WS2 monolayers). Using combined first-principles density-functional theory and nonequilibrium Green's function simulation, we show that the electrical coupling between bilayer-Na3Bi thin film and graphene results in a notable interlayer charge transfer, thus inducing sizable n-type doping in the Na3Bi/graphene heterostructures. In the case of MoS2 and WS2 monolayers, the lateral Schottky transport barrier is significantly lower than for many commonly studied bulk metals, thus revealing bilayer Na3Bi to be a high-efficiency electrical contact material for 2D semiconductors. These findings open up an avenue for utilizing topological semimetal thin film as an electrical contact to 2D materials, and further expand the family of 2D heterostructure devices into the realm of topological materials.