Magnetic Routes to Valley Polarization in Monolayer Transition Metal Dichalcogenides

Abstract

Monolayer transition metal dichalcogenides (TMDs) host two inequivalent valleys at the K and K′ points of the Brillouin zone, offering a binary degree of freedom that can encode information. Lifting the degeneracy between these valleys is the central challenge of valleytronics. In this review, we present the theoretical foundations and experimental progress of magnetic routes to valley polarization in monolayer TMDs. We first develop the relevant theory, including the valley Zeeman effect, spin-valley locking, and the valley Hall effect, before surveying four magnetic mechanisms: external magnetic fields, magnetic proximity effects, magnetic doping, and intrinsic ferrovalley materials. For each mechanism, we compare reported valley splitting energies and operating conditions across a range of material systems. External fields applied to monolayer MX₂ yield modest splittings, while magnetic proximity coupling and doping can enhance the splitting by one to three orders of magnitude. Intrinsic ferrovalley materials such as H-VSe₂ bypass external magnetization entirely, exhibiting spontaneous valley polarization with splittings reaching hundreds of meV and Curie temperatures well above room temperature. We conclude with an outlook on the prospects and remaining challenges for integrating valley polarization into practical information-encoding devices.

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