Hongliang Shi, Hui Pan, Yong-Wei Zhang, Boris I. Yakobson
The quasiparticle (QP) band structures of both strainless and strained monolayer MoS$_{2}$ are investigated using more accurate many body perturbation \emph{GW} theory and maximally localized Wannier functions (MLWFs) approach. For the strainless state, the partially self-consistent \emph{GW$_{0}$} (sc\emph{GW$_{0}$}) calculation demonstrates that monolayer MoS$_{2}$ is a direct semiconductor, consistent with recent experimental observations. By solving the Bethe-Salpeter equation (BSE) including excitonic effects, the predicted optical gap magnitude is consistent with available experimental data. We further predict that the strong exciton binding energy is in the range of 0.50$-$0.40 eV and also is nearly unchanged with increasing strain. In addition, the sc\emph{GW$_{0}$} calculations also predict that monolayer MoS$_{2}$ maintains its direct characteristic under the tensile strain up to 1.41%. As the tensile strain increases further, the electron effective mass decreases, the covalent bonding weakens, and a direct to indirect gap transition occurs. The sc\emph{GW$_{0}$} and BSE calculations are also performed on monolayer WS$_{2}$, similar characteristics are predicted and WS$_{2}$ possesses the lightest effective mass at the same strain among monolayers Mo(S,Se) and W(S,Se). The present calculation results suggest a viable route to tune the electronic properties of monolayer transition-metal dichalcogenides (TMDs) using strain engineering for potential applications in high performance electronic devices.
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http://arxiv.org/abs/1211.5653
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