Optical manipulation and electrical control of valley pseudo-spins in atomically thin semiconductors

Electronic valleys are energy extrema of Bloch bands in momentum space. In analogy to electrons with spin degrees of freedom, valley indices can be considered as pseudo-spins for new modes of electronic and photonic device operation. In this paper, we will review our experimental progress on the investigation of these pseudo-spins using atomically thin semiconductors (MoS2, MoSe2 etc.), which are either monolayer or bilayer group VI transition metal dichalcogenides. We will show that these new 2D semiconductors not only behave as remarkable excitonic systems, but also provide an ideal platform for realizing the optical manipulation and electrical control of valley degrees of freedom.