Peter Christianen, HFML Nijmegen Single-layer transition-metal dichalcogenides, such as MoS2, MoSe2, WS2, WSe2, are two-dimensional semiconductors with a honeycomb lattice. Their band structures show a pair of inequivalent valleys (local extrema) at the +K and -K points of the Brillouin zone. The valleys in the conduction and valence [...]