WS2 in ultrafast laser pulse

We theoretically investigate the interaction of a circularly polarized ultrafast laser pulse with a monolayer of WS2 which belongs to a class of materials known as transition metal dichalcogenides. The applied pulse has a duration of about 4fs. The amplitude of the electric field is about 0.1-0.3 V/Å, and it is comparable to the internal fields acting on electrons. This causes strong interband coupling which results in strong redistribution of electrons between the valence and conduction bands. The monolayer of WS2 has two inequivalent valleys in reciprocal space. We predict that one-cycle circular ultrafast laser pulse populates these valleys unequally leading to the high valley polarization in this monolayer.