Large, valley-exclusive Bloch-Siegert shift in monolayer WS 2

Abstract

Going way off resonance Single atomic layers of transition metal dichalcogenide (TMD) materials have two nonequivalent valleys in their electronic structure. When researchers shine visible light on these monolayers, left-circularly polarized light modifies the electronic levels in one valley but not the other. Sie et al. studied the material WS 2 . They found that in the infrared regime, if the frequency of the light was far away from the resonance, energy levels in both valleys were affected. The so-called Bloch-Siegert effect could explain the energy shift in the “wrong” valley. The findings should be important for the manipulation of valleytronic properties of TMDs. Science , this issue p. 1066