Spin-orbit coupling in the band structure WSe$_{2}$ monolayers

We have mapped the occupied band structure of monolayer WSe$_{2}$ by small spatial spot angle resolved photoemission and have found significant spin-orbit coupling in excess of 500 meV, far larger than for MoS$_{2}$. The experimental band mapping is consistent with theoretical expectations with the top of the valence band is seen at K, not $\Gamma $, thus distinct from the band structure for the bilayer and bulk single crystals. This shift of the top of the valence band in monolayer WSe$_{2}$, from $\Gamma $ to K, is also predicted in density functional theory. In general the wave vector dependent experimental band structure confirms the expectations of density functional theory.