Greetings from Bangkok.
Welcome to hybrid seminars in condensed matter physics at Mahidol University. The seminars are informal and meant to inspire discussions. If you would like to participate, please sign up to receive seminar announcements or contact us at kitinan.pon@mahidol.ac.th.
The seminars start at 13:00 (Thailand time) every Wednesday, unless otherwise announced.
Upcoming Seminar
21.01.2026
Speaker: D.K. Efimkin
Time: 13:00-14:00
Venue: online
Title: Exciton-Polarons in Doped Monolayer Semiconductors
Abstract:
The dynamics of a quasiparticle can be profoundly altered by interactions with the surrounding quantum environment. This general phenomenon—where the particle becomes dressed by excitations of the medium—is broadly referred to as a polaronic effect, a concept introduced by L. Landau and S. Pekar. Historically, the study of Bose polarons, where the medium consists of bosonic excitations such as phonons or magnons, played a foundational role in the development of path integral methods and advanced numerical tools in quantum many-body physics. More recently, the focus has shifted to Fermi polarons, where a mobile impurity interacts with a fermionic bath. This problem has become particularly relevant due to its realization in ultracold atomic gases, enabling precise experimental control and sparking substantial theoretical progress over the past decade.
In this talk, I will present how the exciton-polaron framework successfully captures the optical response of two-dimensional semiconductors under moderate doping. In these systems, photoexcited excitons interact with a Fermi sea formed by excess electrons or holes, leading to the formation of two distinct quasiparticle branches: the attractive and repulsive exciton-polarons. These manifest experimentally as two well-separated peaks in the absorption spectrum. I will discuss how the doping dependence of their resonant energies, spectral weights, and linewidths aligns remarkably well with recent experimental measurements. This agreement high-lights the power of the exciton-polaron theory as a unifying language for describing many-body effects in doped semiconductors, and paves the way for a deeper understanding of quasiparticle behavior in strongly interacting, low-dimensional materials.