Spin-Polarized Electrons in Monolayer MoS$_2$

TL;DR

This study uses optical susceptibility to reveal that electrons in gated monolayer MoS₂ are spin polarized with only two of four bands occupied, driven by strong Coulomb interactions causing spontaneous symmetry breaking.

Contribution

It demonstrates the spin polarization and band occupancy in monolayer MoS₂ using a minimally-invasive optical probe, highlighting Coulomb interactions as the cause.

Findings

Electrons are spin polarized in monolayer MoS₂.

Only two of four bands are occupied, sharing the same spin.

Strong Coulomb interactions facilitate spontaneous symmetry breaking.

Abstract

The optical susceptibility is a local, minimally-invasive and spin-selective probe of the ground state of a two-dimensional electron gas. We apply this probe to a gated monolayer of MoS$_2$. We demonstrate that the electrons are spin polarized. Of the four available bands, only two are occupied. These two bands have the same spin but different valley quantum numbers. We argue that strong Coulomb interactions are a key aspect of this spontaneous symmetry breaking. The Bohr radius is so small that even electrons located far apart in phase space interact, facilitating exchange couplings to align the spins.