Excitons in Atomically Thin TMD in Electric and Magnetic Fields

TL;DR

This paper develops a non-perturbative theory for excitonic magneto-absorption in atomically thin TMDs under strong magnetic fields, revealing new exciton parameters and proposing electric field methods to probe p-wave states for better band structure insights.

Contribution

It introduces a strong-field excitonic theory, revises exciton parameters beyond perturbative estimates, and suggests electric field techniques to access p-wave exciton states in TMDs.

Findings

Perturbative approaches are inadequate for strong magnetic fields.

Revised exciton parameters differ from previous perturbative estimates.

Electric fields can enhance p-wave state visibility in photoluminescence.

Abstract

The magnetic field dependence of photoabsorption provides direct insights into the band structure of semiconductors. It is perhaps surprising that there is a large discrepancy between electron, hole, and reduced mass reported in the recent literature. Motivated by this puzzle we reconsider excitonic magneto-absorption and find that the commonly employed perturbative approach, namely for computing the diamagnetic shift, is inadequate to account for the parameter ranges considered in existing data. In particular, we develop the theory for strong magnetic field and, upon analysis of the data, arrive at the set of exciton parameters different to what has been estimated perturbatively in the literature. Only s-wave excitons are visible in photoluminescence as the spectral weight of p-wave states is too small, this limits the amount of information that can be extracted about the underlying band structure. To overcome this, we propose to study p-wave states by mixing them with s-wave states by external in-plane electric field and show that a moderate DC electric field would provide sufficient mixing to brighten p-wave states. We calculate energies of the p-wave states including the effects of valley-orbital splitting and the orbital Zeeman shift, and show that this provides direct information on the electron-hole mass asymmetry.