Magneto-optics in transition metal diselenide monolayers

TL;DR

This study investigates the magneto-optical properties of MoSe2 and WSe2 monolayers at 4K, revealing how magnetic fields influence valley polarization and Zeeman splitting, with notable differences between the two materials.

Contribution

It provides new insights into valley polarization behavior and Zeeman effects in transition metal diselenide monolayers under magnetic fields, highlighting material-dependent phenomena.

Findings

Valley polarization in MoSe2 can be tuned by magnetic field regardless of laser polarization.

WSe2 shows dependence of trion polarization on both magnetic field and laser helicity.

Both materials exhibit Zeeman splitting of about ±2 meV with g-factors around -4.

Abstract

We perform photoluminescence experiments at 4K on two different transition metal diselenide monolayers, namely MoSe2 and WSe2 in magnetic fields $B_z$ up to 9T applied perpendicular to the sample plane. In MoSe2 monolayers the valley polarization of the neutral and the charged exciton (trion) can be tuned by the magnetic field, independent of the excitation laser polarization. In the investigated WSe2 monolayer sample the evolution of the trion valley polarization depends both on the applied magnetic field and the excitation laser helicity, while the neutral exciton valley polarization depends only on the latter. Remarkably we observe a reversal of the sign of the trion polarization between WSe2 and MoSe2. For both systems we observe a clear Zeeman splitting for the neutral exciton and the trion of about $\pm2$meV at $B_z\mp9$T. The extracted Land\'{e}-factors for both exciton complexes in both materials are $g\approx -4$.