Electronic and optical properties of single-layer MoS2

The electronic structures of a MoS 2 monolayer are investigated with the all-electron first principle calculations based on the density functional theory (DFT) and the spin-orbital couplings (SOCs). Our results show that the monolayer MoS 2 is a direct band gap semiconductor with a band gap of 1.8 eV. The SOCs and d-electrons in Mo play a very significant role in deciding its electronic and optical properties. Moreover, electronic elementary excitations are studied theoretically within the diagrammatic self-consistent field theory. Under random phase approximation, it shows that two branches of plasmon modes can be achieved via the conduction-band transitions due to the SOCs, which are different from the plasmons in a two-dimensional electron gas and graphene owing to the quasi-linear energy dispersion in single-layer MoS 2 . Moreover, the strong optical absorption up to 10 5 cm -1 and two optical absorption edges I and II can be observed. This study is relevant to the applications of monolayer MoS 2 as an advanced photoelectronic device.