Rydberg excitons and polaritons in monolayer transition metal dichalcogenides in a magnetic field

TL;DR

This paper develops a microscopic theory for excitons and polaritons in monolayer TMDs under magnetic fields, accurately capturing strong coupling effects and matching experimental data, while also evaluating interaction strengths.

Contribution

It introduces a numerically exact microscopic approach for excitons and polaritons in TMD monolayers under magnetic fields, surpassing perturbative methods and including strong coupling regimes.

Findings

Excellent agreement with experimental diamagnetic shifts.

Identification of signatures of very strong coupling in polaritons.

Magnetic fields weaken exciton and polariton interactions, with TMDs less affected than quantum wells.

Abstract

We develop a microscopic theory for excitons and cavity exciton polaritons in transition metal dichalcogenide (TMD) monolayers under a perpendicular static magnetic field. We obtain numerically exact solutions for the ground and excited states, accounting for the interplay between arbitrarily large magnetic fields and light-matter coupling strengths. This includes the very strong coupling regime, where light-induced modifications of the exciton wavefunction become essential and the approximate coupled oscillator description breaks down. Our results show excellent agreement with recent experimental measurements of the diamagnetic shift of the ground and excited exciton states in WS$_2$, MoS$_2$, MoSe$_2$, and MoTe$_2$ monolayers. For polaritons, we consider experimentally relevant system parameters and demonstrate that the diamagnetic shifts of both the ground and excited states at high magnetic fields exhibit clear signatures of the very strong coupling regime, highlighting the necessity of our microscopic and numerically exact treatment over perturbative approaches. Furthermore, our microscopic approach allows us to evaluate the exciton-exciton and polariton-polariton interaction strengths. Comparing results specific to TMD monolayers with those applicable to quantum wells, we find that variational approaches overestimate the TMD excitons' interaction strength. We also observe that magnetic fields weaken the interaction strength for both excitons and polaritons, with a less pronounced effect in TMDs than in quantum wells, and that light-induced modifications to the matter component in TMD polaritons can enhance interaction strengths beyond those of purely excitonic interactions.