Thermal effect on magnetoexciton energy spectra in monolayer transition metal dichalcogenides

TL;DR

This paper reveals that thermal motion of excitons in monolayer TMDCs induces a motional Stark effect, significantly shifting energy spectra and altering exciton properties at room temperature, with potential experimental implications.

Contribution

It introduces a novel mechanism where exciton center-of-mass motion affects magnetoexciton energies, including a motional Stark term, previously neglected in studies of TMDCs.

Findings

Thermal-magnetic shifts of a few meV in exciton energies at room temperature.

Change in exciton radius and diamagnetic coefficient due to thermal effects.

Breakdown of SO(2) symmetry leading to new absorption peaks.

Abstract

It is widely comprehended that temperature may cause phonon-exciton scattering, enhancing the energy level's linewidth and leading to some spectrum shifts. However, in the present paper, we suggest a different mechanism that allows the thermal motion of the exciton's center of mass (c.m.) to affect the magnetoexciton energies in monolayer dichalcogenides (TMDCs). By the nontrivial but precise separation of the c.m. motion from an exciton in a monolayer TMDC with a magnetic field, we obtain an equation for the relative motion containing a motional Stark term proportional to the c.m. pseudomomentum, related to the temperature of the exciton gas but neglected in the previous studies. Solving the Schr\"odinger equation without omitting the motional Stark potential at room temperature shows approximately a few meV thermal-magnetic shifts in the exciton energies, significant enough for experimental detection. Moreover, this thermal effect causes a change in exciton radius and diamagnetic coefficient and enhances the exciton lifetime as a consequence. Surprisingly, the thermoinduced motional Stark potential breaks the system's SO(2) symmetry, conducting new peaks in the exciton absorption spectra at room temperature besides those of the $s$ states. This mechanism could be extended for other magnetoquasiparticles such as trions and biexcitons.