Giant and tunable valley degeneracy splitting in MoTe2

TL;DR

This paper demonstrates a method to achieve giant, tunable valley degeneracy splitting in monolayer MoTe2 using proximity-induced Zeeman effect from a EuO substrate, enhancing valleytronic applications.

Contribution

It introduces a novel approach to induce large, controllable valley splitting via proximity effects, surpassing magnetic field limitations.

Findings

Valley splitting over 300 meV achieved in MoTe2/EuO heterostructure.

Valley splitting is tunable by rotating substrate magnetization.

Interband transition energies become valley-dependent, enabling optical control.

Abstract

Monolayer transition-metal dichalcogenides possess a pair of degenerate helical valleys in the band structure that exhibit fascinating optical valley polarization. Optical valley polarization, however, is limited by carrier lifetimes of these materials. Lifting the valley degeneracy is therefore an attractive route for achieving valley polarization. It is very challenging to achieve appreciable valley degeneracy splitting with applied magnetic field. We propose a strategy to create giant splitting of the valley degeneracy by proximity-induced Zeeman effect. As a demonstration, our first principles calculations of monolayer MoTe$_2$ on a EuO substrate show that valley splitting over 300 meV can be generated. The proximity coupling also makes interband transition energies valley dependent, enabling valley selection by optical frequency tuning in addition to circular polarization. The valley splitting in the heterostructure is also continuously tunable by rotating substrate magnetization. The giant and tunable valley splitting adds a readily accessible dimension to the valley-spin physics with rich and interesting experimental consequences, and offers a practical avenue for exploring device paradigms based on the intrinsic degrees of freedom of electrons.