Laser energy dependence of valley polarization in transition-metal dichalcogenides

Photoabsorption spectra by circular polarized light in transition-metal dichalcogenides are calculated as a function of laser excitation energy. Although the 100% valley polarization occurs at the K point of the Brillouin zone, the difference of the absorption intensity for left-handed and right-handed circular polarized light becomes maximum at about 1 eV higher energy than the direct energy band gap. The maximum intensity difference corresponds to the so-called Λ valley in the Brillouin zone. In order to understand valley polarization, analytic formula of optical absorption is given by tight-binding method.