Spin–orbit coupling in the band structure of monolayer WSe2

The potential of monolayer WSe₂ as a two-dimensional conductor in spintronic devices has been much discussed. Part of the attraction of WSe₂ is that it is a layered system and, as with graphene, single-layer sheets can be fabricated or transferred onto insulating substrates. Unlike graphene, WSe₂ monolayers have a very large spin–orbit coupling and a band gap. Even though the large spin–orbit coupling splitting at the top of the valence band at point (Δ_SOC) of single-layer WSe₂ has attracted considerable attention in various theoretical efforts, there has been very little comparison with experiment. We used ARPES to map out the band structure of single-layer micro flake WSe₂.

The splitting of the top of the valence band because of spin–orbit coupling is 513 ± 10 meV, in general agreement with theoretical predictions and in the same range as that of bulk WSe₂. Overall, our density functional theory (DFT) calculations of the band structure are in excellent agreement with the ARPES results. We have verified that the few discrepancies between theory and experiment are not due to the effect of strain.