Crossover from exciton polarons to trions in doped two-dimensional semiconductors at finite temperature

TL;DR

This paper investigates how temperature influences the optical properties of doped two-dimensional semiconductors, revealing a crossover from polaron quasiparticles to trion states and analyzing the implications for light-matter interactions.

Contribution

It introduces a finite-temperature Fermi-polaron theory to describe the crossover from polaron quasiparticles to trions in doped 2D semiconductors, highlighting qualitative changes in optical spectra.

Findings

Crossover from polaron to trion regimes with increasing temperature or decreasing doping.

Evolution of emission profile from symmetric Lorentzian to asymmetric with exponential tail.

Existence of well-defined polariton quasiparticles despite polaron destruction.

Abstract

We study systematically the role of temperature in the optical response of doped two-dimensional semiconductors. By making use of a finite-temperature Fermi-polaron theory, we reveal a crossover from a quantum-degenerate regime with well-defined polaron quasiparticles to an incoherent regime at high temperature or low doping where the lowest energy "attractive" polaron quasiparticle is destroyed, becoming subsumed into a broad trion-hole continuum. We demonstrate that the crossover is accompanied by significant qualitative changes in both absorption and photoluminescence. In particular, with increasing temperature (or decreasing doping), the emission profile of the attractive branch evolves from a symmetric Lorentzian to an asymmetric peak with an exponential tail involving trions and recoil electrons at finite momentum. We discuss the effect of temperature on the coupling to light for structures embedded into a microcavity, and we show that there can exist well-defined polariton quasiparticles even when the exciton-polaron quasiparticle has been destroyed, where the transition from weak to strong light-matter coupling can be explained in terms of the polaron linewidths and spectral weights.