Optical investigation of monolayer and bulk tungsten diselenide (WSe$_{2}$) in high magnetic fields

TL;DR

This study uses high magnetic field optical spectroscopy to compare carrier behaviors in monolayer and bulk WSe$_{2}$, revealing distinct excitonic and valley splitting phenomena.

Contribution

It provides a detailed analysis of the magnetic field effects on excitons and carriers in monolayer versus bulk WSe$_{2}$, highlighting different physical models applicable to each.

Findings

Monolayer WSe$_{2}$ exhibits linear exciton shifts and valley splitting.

Bulk WSe$_{2}$ shows excitonic absorption and spin splitting.

Different models (Dirac-like and hydrogen) describe the carrier behaviors.

Abstract

Optical spectroscopy in high magnetic fields $B\leq65$ T is used to reveal the very different nature of carriers in monolayer and bulk transition metal dichalcogenides. In monolayer WSe$_{2}$, the exciton emission shifts linearly with the magnetic field and exhibits a splitting which originates from the magnetic field induced valley splitting. The monolayer data can be described using a single particle picture with a Dirac-like Hamiltonian for massive Dirac fermions, with an additional term to phenomenologically include the valley splitting. In contrast, in bulk WSe$_{2}$ where the inversion symmetry is restored, transmission measurements show a distinctly excitonic behavior with absorption to the 1s and 2s states. Magnetic field induces a spin splitting together with a small diamagnetic shift and cyclotron like behavior at high fields, which is best described within the hydrogen model.