Long tailed trions in monolayer MoS2: Temperature dependent asymmetry and resulting red-shift of trion photoluminescence spectra

Abstract

Monolayer molybdenum disulfide (MoS2) has emerged as a model system for studying many-body physics because the low dimensionality reduces screening leading to tightly bound states stable at room temperature. Further, the many-body states possess a pseudo-spin degree of freedom that corresponds with the two direct-gap valleys of the band structure, which can be optically manipulated. Here we focus on one 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 and peak position that differs from the zero momentum trion energy. The asymmetry of the trion PL peak and resulting peak red-shift depends both on the trion size and a temperature-dependent contribution. Ignoring the trion asymmetry will result in over estimating the trion binding energy by nearly 20 meV at room temperature. We analyze the temperature-dependent PL to reveal the effective trion size, consistent with the literature, and the temperature dependence of the band gap and spin-orbit splitting of the valence band. This is the first time the temperature-dependence of the trion PL has been analyzed with such detail in any system.

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

“…1(c)] yields E G ð0Þ ¼ 1.943 eV, S ¼ 1.87, and hℏwi ¼ 24.2 AE 1.5 meV. The coupling constant and the average phonon energy are similar to those reported previously in the literature for the TMDC ML family [25,34,41,70,71]. The evolution of the linewidth as a function of temperature is shown in Fig.…”

Temperature dependence of the double‐resonance Raman bands in monolayer MoS2

“…Figure a shows the fitting of the PL spectra at T = 173 K using four Voigt components. The most intense feature, named T A , is associated with the A trion . The strong intensity of T A is due to the excess of charge (possible optical doping) induced by the relatively high laser power used in our experiments .…”

“…The strong intensity of T A is due to the excess of charge (possible optical doping) induced by the relatively high laser power used in our experiments . The two smaller bands, better observed in Figure a, are named X A and X B and associated with the A and B excitons, respectively. The positions of T A , X A , and X B as a function of temperature are shown in Figure b and were fitted according to the equation: where E X ( T = 0) is the extrapolated band gap at 0 K, a is a fitting parameter, and Θ is an average phonon energy .…”

Dark excitations in monolayer transition metal dichalcogenides

“…In particular, it is not obvious which states contribute to the different features observed in the measured spectra. Furthermore, environmental screening [34] and finite temperature effects [36] can reduce the trion binding energies. We also note that our calculations are performed for vanishing doping concentration.…”