Realization of valley-spin polarized current via parametric pump in monolayer $\rm MoS_2$

TL;DR

This paper demonstrates how adiabatic electron pumping can generate tunable valley-spin polarized currents in monolayer MoS2 by breaking degeneracy with an exchange field and controlling phase differences, revealing resonant behaviors.

Contribution

It introduces a novel device setup that achieves simultaneous valley-spin polarized current generation via parametric pumping in monolayer MoS2, with detailed analysis of parameter effects.

Findings

Pumped currents are tunable by phase difference of potentials.

Resonant peaks in current depend on system size.

Current oscillates periodically with system length.

Abstract

Monolayer $MoS_2$ is a typical valleytronic material with valley-spin locked valence bands. We numerically investigate the valley-spin polarized current in monolayer $\rm MoS_2$ via adiabatic electron pumping. By introducing an exchange field to break the energy degeneracy of monolayer $MoS_2$, the top of its valence bands is valley-spin polarized and tunable by the exchange field. A device with spin-up polarized left lead, spin-down polarized right lead, and untuned central region is constructed through applying different exchange fields in the corresponding regions. Then, equal amount of pumped currents with opposite valley-spin polarization are simultaneously generated in the left and right leads when periodically varying two pumping potentials. Numerical results show that the phase difference between the pumping potentials can change the direction and hence polarization of the pumped currents. It is found that the pumped current exhibits resonant behavior in the valley-spin locked energy window, which depends strongly on the system size and is enhanced to resonant current peaks at certain system lengths. More importantly, the pumped current periodically oscillates as a function of the system length, which is closely related to the oscillation of transmission. The effects of other system parameters, such as the pumping amplitude and the static potential, are also thoroughly discussed.