Long tailed trions in monolayer MoS$_2$: Temperature dependent asymmetry and red-shift of trion photoluminescence spectra

TL;DR

This study investigates the temperature-dependent asymmetry and red-shift in the photoluminescence spectra of negatively charged trions in monolayer MoS$_2$, revealing insights into trion size, band gap, and decay mechanisms.

Contribution

The paper introduces a method to accurately separate exciton and trion contributions in PL spectra by analyzing the asymmetric tail, and explores temperature effects on trion properties in monolayer MoS$_2$.

Findings

Trion PL peaks exhibit a long low-energy tail due to non-zero momentum decay.

Temperature analysis yields effective trion size consistent with literature.

Signatures of Pauli-blocking influence trion decay processes.

Abstract

Monolayer molybdenum disulfide (MoS$_2$) has emerged as an excellent 2D model system because of its two inequivalent, direct-gap valleys that lead to exotic bound and excited states. Here we focus on one such bound state, the negatively charged trion. Unlike excitons, trions can radiatively decay with non-zero momentum by kicking out an electron, resulting in an asymmetric trion photoluminescence (PL) peak with a long low-energy tail. As a consequence, the peak position does not correspond to the zero momentum trion energy. By including the trion's long tail in our analysis we are able to accurately separate the exciton from the trion contributions to the PL spectra. According to theory, the asymmetric energy tail has both a size-dependent and a temperature-dependent contribution. Analysis of the temperature-dependent data reveals the effective trion size, consistent with literature, and the temperature dependence of the band gap and spin-orbit splitting of the valence band. Finally, we observe signatures of Pauli-blocking of the trion decay.