Strongly interaction-enhanced valley magnetic response in monolayer WSe2

TL;DR

This study reveals a strongly enhanced valley magnetic response in monolayer WSe2 due to electron interactions, showing a nonlinear valley Zeeman effect and a significant increase in exciton g-factor linked to many-body effects.

Contribution

It demonstrates a nonlinear valley Zeeman effect and a fourfold exciton g-factor enhancement in monolayer WSe2, highlighting the role of strong electron interactions in 2D materials.

Findings

Observation of nonlinear valley Zeeman effect.

Fourfold increase in exciton g-factor.

No saturation of enhancement at lower temperatures.

Abstract

Coulomb interaction between electrons lies at the heart of magnetism in solids. In contrast to conventional two-dimensional (2D) systems, electrons in monolayer transition metal dichalcogenides (TMDs) possess coupled spin and valley degrees of freedom by the spin-orbit interaction. The electrons are also strongly interacting even in the high-density regime because of the weak dielectric screening in two dimensions and a large band mass. The combination of these properties presents a unique platform for exploring spin and valley magnetism in 2D electron liquids. Here we report an observation by magneto-photoluminescence spectroscopy of a nonlinear valley Zeeman effect, correlated with an over fourfold enhancement in the exciton g-factor in monolayer WSe2. The effect occurs when the Fermi level crosses the spin-split upper conduction band, corresponding to a change of the spin-valley degeneracy from 2 to 4. The enhancement increases, shows no sign of saturation as the sample temperature decreases. Our result suggests the possibility of rich many-body ground states in monolayer TMDs with multiple internal degrees of freedom.