Michael N. Leuenberger
University of Central Florida, USA
Biography
Single layer (SL) transition metal dichalcogenides (TMDCs) (MX2; M=transition metal such as Mo, W and X= S, Se, Te) have attracted a lot of attention due to their intriguing electronic and optical properties. SL TMDCs are direct band gap semiconductors, which can be used to produce smaller and more energy efficient devices such as transistors and integrated circuits. Moreover, the band gap lie in the visible region, which makes them highly responsive when exposed to visible light, a property with potential applications in optical detection. In contrast to graphene, SL TMDCs exhibit large spin-orbit coupling (SOC) originating from the d orbitals of the transition metal atoms. The presence of the giant SOC makes them great candidates for exploring spin physics and for spintronic devices. Defects usually play an important role in tailoring electronic, optical and magnetic properties of semiconductors. We performed standard first-principle study to evaluate the electronic and optical properties of single-layer (SL) transition metal dichalcogenides (TMDCs), in the presence of vacancy defects (VDs). We consider three types of VDs in SL TMDCs (1) X-vacancy, (2) X2-vacancy, and (3) M-vacancy. We find that VDs lead to localized defect states (LDS) in the band structure, which in turn give rise to sharp transitions in in-plane and out-of-plane optical susceptibilities, cII and c^, respectively. The effects of spin orbit coupling (SOC) are also considered. We find that SOC splitting in LDS is directly related to the atomic number of the transition metal atoms. Apart from electronic and optical properties we also find magnetic signatures (local magnetic moment of ~µB) in MoSe2 in the presence of Mo vacancy, which breaks the time reversal symmetry and therefore lifts the Kramers degeneracy. We use group theory to derive the optical selection rules for both cII and c^.