Valley-dependent transport through graphene quantum dots due to proximity-induced, staggered spin-orbit couplings

TL;DR

This paper investigates how proximity-induced spin-orbit couplings in graphene with quantum dot arrays can be used to control valley-dependent transport, enabling valley polarization and localization for potential valleytronic applications.

Contribution

It demonstrates how tuning staggered SOCs and gate voltages in graphene heterostructures can manipulate valley currents and states, offering new methods for valleytronics.

Findings

Rashba coupling controls valley properties in weak SOC regimes.

Gate voltage can switch valley polarization and scattering.

Proper SOC tuning localizes valley states around IQDs.

Abstract

We study a system composed of graphene decorated with an array of islands with C_3v symmetry that induce quantum dot (IQD) regions via proximity effects and give rise to several spin-orbit couplings (SOCs). We evaluate transport properties for an array of IQDs and analyze the conditions for realizing isolated valley conductances and valley-state localization. The resulting transmission shows a square-type behavior with wide gaps that can be tuned by adjusting the strength of the staggered intrinsic SOCs. Realistic proximity effects are characterized by weak SOC strengths, and the analysis of our results in this regime shows that the Rashba coupling is the important interaction controlling valley properties. As a consequence, a top gate voltage can be used to tune the valley polarization and switch the valley scattering for positive or negative incident energies. A proper choice of SOC strengths leads to higher localization of valley states around the linear array of IQDs. These systems can be implemented in heterostructures composed of graphene and semiconducting transition-metal dichalcogenides (TMDs) such as MoSe2, WSe2, MoS2, or WS2. In these setups, the magnitudes of induced SOCs depend on the twist angle, and due to broken valley degeneracy, valley-polarized currents at the edges can be generated in a controllable manner as well as localized valley states. Our findings suggest an alternative approach for producing valley-polarized currents and propose a corresponding mechanism for valley-dependent electron optics and optoelectronic devices.