Electric control of valley polarization in monolayer WSe2 using a van der Waals magnet

A ferromagnetic tunnelling contact enables electrically controlled valley polarization in monolayer WSe2. Electrical manipulation of the valley degree of freedom in transition metal dichalcogenides is central to developing valleytronics. Towards this end, ferromagnetic contacts, such as Ga(Mn)As and permalloy, have been exploited to inject spin-polarized carriers into transition metal dichalcogenides to realize valley-dependent polarization. However, these materials require either a high external magnetic field or complicated epitaxial growth steps, limiting their practical applications. Here we report van der Waals heterostructures based on a monolayer WSe2 and an Fe3GeTe2/hexagonal boron nitride ferromagnetic tunnelling contact that under a bias voltage can effectively inject spin-polarized holes into WSe2, leading to a population imbalance between +/- K valleys, as confirmed by density functional theory calculations and helicity-dependent electroluminescence measurements. Under an external magnetic field, we observe that the helicity of electroluminescence flips its sign and exhibits a hysteresis loop in agreement with the magnetic hysteresis loop obtained from reflective magnetic circular dichroism characterizations on Fe3GeTe2. Our results could address key challenges of valleytronics and prove promising for van der Waals magnets for magneto-optoelectronics applications.

Automated summary

This study presents a new method for electrically controlled valley polarization based on van der Waals heterostructures. By utilizing a ferromagnetic tunnelling contact of Fe3GeTe2/hexagonal boron nitride, spin-polarized holes can be effectively injected into monolayer WSe2, resulting in a population imbalance between the +/- K valleys. Under an external magnetic field, the helicity of electroluminescence flips its sign, consistent with the magnetic hysteresis loop of Fe3GeTe2.