Spin and valley physics in 2D transiton metal dichalcogenides

Abstract

The Bloch bands in many crystals have a degenerate set of energy extrema in momentum space known as valleys. For band-edge carriers, the valley index becomes a discrete degree of freedom in addition to spin. In this talk, I will show that in monolayer transition metal dichalcogenides, the pair of valleys which are time-reversal of each other are distinguishable by their opposite values of magnetic moment, Berry curvature, and circularly-polarized optical transition selection rule. This allows the use of valley pseudospin as information carrier for valley based electronics. I will discuss mechanisms to generate and control the spin and valley pseudospin currents, which are at the heart of spin and valley based electronics. These include the valley and spin Hall effects and the nonlinear valley and spin currents response. I will also discuss the valley physics of novel exciton systems in monolayers and heterobilayers.