Valley Polarization in Transition-Metal Dichalcogenides by Optical Pumping

Abstract

Degenerate valleys of energy bands well separated in momentum space constitute a discrete degrees of freedom for low-energy electrons. This has led to the emergence of valleytronics, a conceptual electronics based on manipulating valley index. Transition-metal dichalcogenides monolayers have been theoretically proposed as a good platform to realize manipulation of valley degrees of freedom through nonzero Berry curvatures at high symmetric points in Brillouin zone. Very recently several groups reported the selective occupation of the degenerate but inequivalent valleys by circularly polarized optical pumping in transition-metal dichalcogenides monolayers. These experimental evidences reveal the viability of optical valley control in group-VI transition-metal dichalcogenides, and form the basis for integrated valleytronics and spintronics application.