Doping And Adsorption Control Of Electron Spin And Valley Degree Of Freedom In Two-dimensional Materials

In this paper,we study the spin and valley splitting of the transition-metal atoms adsorbed transition-metal dichalcogenide monolayer and MnPSe3 monolayer with atom doping by the first-principles calculations based on density functional theory.And we find in these systems the spin and valley related physics,which provides important theoretical support for the realization of spin and valley polarization.For the monolayer MX2,the inversion symmetry breaking together with the strong SOC lifts the spin degeneracy of energy bands and makes it have peculiar coupled spin and valley physics.However,the time-reversal symmetry requires that the spin splitting in opposite valleys must be opposite.Therefore,the valley is still degenerate when SOC is considered.We propose a strategy to realize valley splitting by adsorbing transition-metal atoms.The local magnetic moments are introduced into the system when the transition-metal atoms are adsorbed on the monolayer surface.The Zeeman effect arising from the local magnetic moment at transition-metal atom sites lifts the valley degeneracy.Due to the valley splitting,we can selectively dope only one valley with carriers.Under the action of in-plane electric field and Berry curvature,the carrries will produce an anomalous charge/spin/valley Hall effect.The valley splitting depends on the direction of magnetization and thus can be tuned continuously by an external magnetic field.We take monolayer MoS2 as an example to show our detailed results from first-principles calculation.The monolayer MnPX3 has two unequal valleys in the momentum space.When SOC effect is considered,the valley degeneracy can be lifted,but the antiferromagnetic coupling makes the spin in the entire momentum space degenerate.We propose a strategy to realize simultaneously the spin and valley splitting by doping-induced Zeeman field in monolayer MnPX3.We study the electronic structures of the transition-metal atoms doped monolayer MnPSe3,as well as the spin and valley related physics by the first-principles calculations method.We demonstrate that in the Zn-doped monolayer MnPSe3 the valley splitting larger than 20 meV and spin splitting lager than 100 meV can be achieved simultaneously.The doping-induced spin and valley splitting is attractive for spintronics and valleytronics as it creates differences in various energy scales between the valleys and between spins,which will facilitate the access and manipulation of valley and spin degrees of freedom by electric gating in addition to optic pumping.