Optical spin injection in MoS2 monolayers

Two-dimensional transition-metal dichalcogenide materials have recently attracted great attention from the scientific community due to their interesting properties such as the presence of an energy band gap and the support of spin-polarized states. In particular, monolayer molybdenum disulfide has a structure with no inversion symmetry and, thus, presents a large spin-splitting of the top valence bands. This latter fact makes it favorable for studies of optical spin injection, a phenomenon that, under incidence of circularly polarized light, creates spin-polarized electrons in the conduction bands. Here, we perform a theoretical study of the one-photon optical spin and current injection on transition-metal dichalcogenide monolayers of molybdenum disulfide. In particular, we present calculations for spectra of the degree of spin polarization, which are calculated in a full-band structure scheme employing density functional theory; besides the so-called quasiparticle GW approximation is applied for the calculation of the band gap energy correction. Our results show 100% of spin polarization of the electrons for the one monolayer structure at the K valley. The degree of spin polarization also presents a net maximum value at the direct energy band gap at K as the number of monolayers increases.