Spin–orbit splitting in the valence bands of 1<i>T</i>-TaS₂ and 1<i>T</i>-TaSe₂

We perform angle-resolved photoemission spectroscopy on 1<i>T</i>-TaS₂ and 1<i>T</i>-TaSe₂ using synchrotron radiation. We observe a characteristic splitting of the chalcogen p-derived valence bands along high symmetry directions. Density functional theory calculation and group theory strongly suggest that this splitting is due to spin–orbit interaction along one direction, and to symmetry along the other direction. We note that, according to the Kramers degeneracy, the spin–orbit interaction leaves every state doubly degenerate. Furthermore, this study allows us to identify a mixing between bands with Ta 5d and Se 4p character, possibly relevant for the different temperature behaviours of the two compounds.