Valley Polarization by Spin Injection in a Light-Emitting van der Waals Heterojunction

TL;DR

This paper demonstrates spin injection into a TMDC heterojunction, achieving controllable valley polarization and circularly polarized light emission, advancing the development of spin-valleytronic devices without optical excitation.

Contribution

It introduces a method for electronic control of valley polarization via spin injection in TMDC heterojunctions, enabling new spin-valleytronic device functionalities.

Findings

Spin injection from ferromagnetic electrodes into TMDC heterojunctions.

Magnetic field tuning of valley polarization and light emission.

Observation of spin-polarized hole transport within WSe2.

Abstract

The band structure of transition metal dichalcogenides (TMDCs) with valence band edges at different locations in the momentum space could be harnessed to build devices that operate relying on the valley degree of freedom. To realize such valleytronic devices, it is necessary to control and manipulate the charge density in these valleys, resulting in valley polarization. While this has been demonstrated using optical excitation, generation of valley polarization in electronic devices without optical excitation remains difficult. Here, we demonstrate spin injection from a ferromagnetic electrode into a heterojunction based on monolayers of WSe2 and MoS2 and lateral transport of spin-polarized holes within the WSe2 layer. The resulting valley polarization leads to circularly polarized light emission which can be tuned using an external magnetic field. This demonstration of spin injection and magnetoelectronic control over valley polarization provides a new opportunity for realizing combined spin and valleytronic devices based on spin-valley locking in semiconducting TMDCs.