Optically Controlled Valley Filter and Transistor Based on Transition-Metal Dichalcogenide Planar Heterojunctions

Abstract

In this work, we theoretically explore the spin- and valley-resolved transport in monolayer transition-metal dichalcogenide (TMDC) planar heterojunctions. We propose two types of ${\mathrm{Mo}\mathrm{S}}_{2}{/\mathrm{WS}}_{2}$ planar heterojunctions based on the position of the optical modulation. Spin- and valley-resolved transmission is realized and transmission spectra look quite different between the two types of heterojunctions due to the spin-valley-dependent effective potential, which results from the off-resonant circularly polarized light (CPL) and the band offset. Specifically, fully valley-polarized transport is demonstrated in Type-1 heterojunction (optical modulation on ${\mathrm{WS}}_{2}$). However, transmission in Type-2 heterojunction (optical modulation on ${\mathrm{Mo}\mathrm{S}}_{2}$) experiences a dramatic change with respect to CPL intensity, where the system can be switched from perfect valley-polarized ``on'' state to nearly nonpolarized ``off'' state only by adjusting the CPL intensity. As a result, we propose pure optically controlled valley filter and valley transistor based on the two types of planar heterojunctions, respectively. This work may shed light on potential application of valleytronic devices based on TMDC planar heterojunctions.