Electrically tunable valley dynamics in twisted WSe$_2$/WSe$_2$ bilayers

TL;DR

This paper demonstrates how the twist angle in WSe$_2$/WSe$_2$ bilayers can be used to electrically control valley dynamics, including polarization and lifetime, opening new possibilities for valleytronic devices.

Contribution

It introduces a method to tune valley polarization and lifetime in twisted bilayers through electrostatic doping, revealing a new degree of control in valleytronics.

Findings

High circular polarization (>60%) of interlayer excitons at zero fields.

Valley lifetime exceeds 40 ns and can be tuned by over three orders of magnitude.

Electrostatic doping switches DOCP from ~80% in n-doped to <5% in p-doped regimes.

Abstract

The twist degree of freedom provides a powerful new tool for engineering the electrical and optical properties of van der Waals heterostructures. Here, we show that the twist angle can be used to control the spin-valley properties of transition metal dichalcogenide bilayers by changing the momentum alignment of the valleys in the two layers. Specifically, we observe that the interlayer excitons in twisted WSe$_2$/WSe$_2$ bilayers exhibit a high (>60%) degree of circular polarization (DOCP) and long valley lifetimes (>40 ns) at zero electric and magnetic fields. The valley lifetime can be tuned by more than three orders of magnitude via electrostatic doping, enabling switching of the DOCP from ~80% in the n-doped regime to <5% in the p-doped regime. These results open up new avenues for tunable chiral light-matter interactions, enabling novel device schemes that exploit the valley degree of freedom.