题目：Valley Effects on Molybdenum Disulfide---MoS2
报告人：李伟
时间：2015.04.17
地点：固体所新楼520会议室
摘要：
Degenerate valleys of energy bands well separated in momentum space constitute a discrete degrees of freedom for low-energy electrons. With the emergence of graphene, the concept of valleytronics based on manipulating the valley index has attracted great interests. 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. MoS_2 monolayers have two important distinctions from graphene. First, inversion symmetry is explicitly broken , which can give rise to the valley Hall effect and lead to valley-dependent optical selection rules for interband transitions at K points. Second, MoS_2 has a strong spin-orbit coupling (SOC) originated from the d-orbitals of the Mo atoms, and can be an interesting platform to explore spin physics and spintronics applications. The absence of inversion symmetry is the ultimate source of chirality which can lead to completely valley polarization. Very recently several groups reported the selective occupation of the degenerate but inequivalent valleys by circularly polarized optical pumping, stress or magnetic field 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.
The effect of a perpendicular magnetic field on the electronic structure and charge transport of a monolayer MoS_2 nanoribbon at zero temperature has been studied in this report. First, the effective two-band Hamiltonian provides a mismatch between the valley Zeeman coupling in the conduction and valence bands due to the effective mass asymmetry. Second, we investigate the transport properties of the system by calculating the spin-valley resolved conductance with and without disorder.
