Should the optical response of doped two-dimensional semiconductors be described within a Fermi-polaron or a trion model? IFIMAC member Francesca Maria Marchetti in collaboration with Antonio Tiene at UAM and researchers at Monash University have recently published two joint articles in Physical Review B (Editors’ Suggestion) and Physical Review Letters tackling this question.
Using a finite-temperature Fermi-polaron theory, the authors demonstrate a crossover from a quantum degenerate regime with a well-defined polaron quasiparticle to an incoherent regime at high temperature or low doping, where the lowest energy attractive polaron becomes subsumed into a broad trion-hole continuum. The crossover is accompanied by a characteristic evolution of the emission profile, from a symmetric Lorentzian to an asymmetric peak.
Further, by introducing a quantum virial expansion for the system optical response, the authors have been able to obtain exact analytic expressions for the photoluminescence and to formally unify the two distinct theoretical pictures that have been applied to this system. In particular, the authors have revealed that the predictions of the conventional trion picture correspond to a high-temperature and weak-interaction limit of Fermi-polaron theory. The theoretical results have been demonstrated to be in excellent agreement with recent experiments on doped monolayer MoSe2.
Full articles can be found here: