Excitonic valley effects in monolayer WS$_2$ under high magnetic fields

TL;DR

This study explores how high magnetic fields influence valley polarization and excitonic properties in monolayer WS$_2$, revealing insights into quasiparticle behavior and valley splitting in 2D semiconductors.

Contribution

It provides experimental evidence of valley degeneracy lifting and g factor determination for excitons and trions in monolayer WS$_2$ under high magnetic fields.

Findings

Valley degeneracy is lifted for all optical features.

Diamagnetic shifts reveal quasiparticle size.

Valley polarization effects match theoretical predictions.

Abstract

Transition-metal dichalcogenides can be easily produced as atomically thin sheets, exhibiting the possibility to optically polarize and read out the valley pseudospin of extremely stable excitonic quasiparticles present in these 2D semiconductors. Here, we investigate a monolayer of tungsten disulphide in high magnetic fields up to 30\,T via photoluminescence spectroscopy at low temperatures. The valley degeneracy is lifted for all optical features, particularly for excitons, singlet and triplet trions, for which we determine the g factor separately. While the observation of a diamagnetic shift of the exciton and trion resonances gives us insight into the real-space extension of these quasiparticles, magnetic field induced valley polarization effects shed light onto the exciton and trion dispersion relations in reciprocal space. The field dependence of the trion valley polarizations is in line with the predicted trion splitting into singlet and triplet configurations.