Electron Transport in MoWSeS Monolayers in Presence of an External   Electric Field
  The influence of an external electric field on single-layer transition-metal dichalcogenides TX2 with T = Mo, W and X = S, Se (MoWSeS) have been investigated by means of density-functional theory within two-dimensional periodic boundary conditions under consideration of relativistic effects including the spin-orbit interactions. Our results show that the external field modifies the band structure of the monolayers, in particular the conduction band. This modification has, however, very little influence on the band gap and effective masses of holes and electrons at the K point, and also the spin-orbit splitting of these monolayers is almost unaffected. Our results indicate a remarkable stability of the electronic properties of TX2 monolayers with respect to gate voltages. A reduction of the electronic band gap is observed only starting from field strengths of 2.0 V per {\AA} (3.5 V per {\AA}) for selenides (sulphides), and the transition to a metallic phase would occur at fields of 4.5 V per {\AA} (6.5 V per {\AA}). 
Nourdine Zibouche, Pier Philipsen, Thomas Heine and Agnieszka Kuc
cond-mat.mtrl-sci