# Revealing exciton masses and dielectric properties of monolayer semiconductors with high magnetic fields

## TL;DR

This study uses high magnetic field optical spectroscopy to measure exciton masses and dielectric properties in monolayer transition-metal dichalcogenides, providing key parameters for optoelectronic applications.

## Contribution

It presents the first high-field absorption spectroscopy measurements of multiple excitonic states in monolayer TMDs up to 91 T, directly revealing exciton masses and dielectric properties.

## Key findings

- Exciton masses are heavier than theoretical predictions, especially in Mo-based monolayers.
- Provides direct measurements of exciton binding energies and radii.
- Determines free-particle bandgaps in monolayer TMDs.

## Abstract

In semiconductor physics, many essential optoelectronic material parameters can be experimentally revealed via optical spectroscopy in sufficiently large magnetic fields. For monolayer transition-metal dichalcogenide semiconductors, this field scale is substantial --tens of teslas or more-- due to heavy carrier masses and huge exciton binding energies. Here we report absorption spectroscopy of monolayer MoS$_2$, MoSe$_2$, MoTe$_2$, and WS$_2$ in very high magnetic fields to 91~T. We follow the diamagnetic shifts and valley Zeeman splittings of not only the exciton's $1s$ ground state but also its excited $2s$, $3s$, ..., $ns$ Rydberg states. This provides a direct experimental measure of the effective (reduced) exciton masses and dielectric properties. Exciton binding energies, exciton radii, and free-particle bandgaps are also determined. The measured exciton masses are heavier than theoretically predicted, especially for Mo-based monolayers. These results provide essential and quantitative parameters for the rational design of opto-electronic van der Waals heterostructures incorporating 2D semiconductors.