Magneto-Optical Measurements of the Negatively Charged 2$s$ Exciton in WSe$_2$

Abstract

Monolayer transition metal dichalcogenides host a variety of optically excited quasiparticles species that stem from two-dimensional confinement combined with relatively large carrier effective masses and reduced dielectric screening. The magnetic response of these quasiparticles gives information on their spin and valley configurations, nuanced carrier interactions, and insight into the underlying band structure. Recently, there have been several reports of 2$s$/3$s$ charged excitons in TMDs, but very little is still known about their response to external magnetic fields. Using photoluminescence excitation spectroscopy, we observe the presence of the 2$s$ charged exciton and report for the first time its response to an applied magnetic field. We benchmark this response against the neutral exciton and find that both the 2$s$ neutral and charged excitons exhibit similar behavior with g-factors of g$_{\rm{X_0^{2s}}}$=-5.20$\pm$0.11 and g$_{\rm{X_-^{2s}}}$=-4.98$\pm$0.11, respectively.