The Joint Condensed Matter Seminar (JCMS) series is organised by KTH Royal Insitute of Technology, Nordita, and Stockholm University.
On Friday, September 15th, 2023 from 11 am to 12 am we will host a seminar by Raül Perea Causín from Chalmers University of Technology.
Microscopic theory of charge complexes in atomically thin materials
Atomically thin materials have emerged as the most promising two-dimensional platform for future optoelectronic applications and for the study of quantum many-body physics. In particular, transition metal dichalcogenides (TMDs) exhibit strong Coulomb interaction, resulting in the formation of tightly-bound electron-hole complexes that dominate optics, dynamics, and transport [1]. In the neutral regime, excitons – bound electron-hole pairs – constitute the dominating many-particle species from low to moderate photoexcitation densities. In the presence of doping, however, excitons can bind to additional charges and form trions. In order to achieve an efficient and controllable implementation of TMDs in novel devices, understanding the fundamental properties of excitons and trions in these materials is crucial.
In this work, we provide a microscopic understanding of the underlying many-particle mechanisms that govern the operation of TMD optoelectronic devices. Based on the density-matrix formalism, we describe the dynamics in a system of interacting electrons, holes, phonons, and photons. We unveil the formation dynamics of so-called dark excitons [2] and resolve the main pathways of the phonon-assisted dissociation of excitons into unbound electron-hole pairs [3]. Furthermore, we tackle the problem of exciton diffusion, tracing the emergence of photoluminescence halos [4] back to the large heating and thermal drift of excitons that occur at strong photoexcitation [5]. Finally, we consider doped TMDs and investigate the trion dynamics, including diffusion and photoluminescence [6,7]. In particular, we predict so far unobserved luminescence signatures that could shed light on the internal structure of trions.
Overall, this work provides microscopic insights into many-particle processes governing the optics, dynamics, and transport in atomically thin semiconductors.
[1] APL Mater 10, 100701 (2022)
[2] Nano Lett. 21, 5867 (2021)
[3] Nanoscale 13, 1884 (2021)
[4] Phys. Rev. Lett. 120, 207401 (2018)
[5] Nano Lett. 19, 7317 (2019)
[6] Phys. Rev. B 106, 115407 (2022)
[7] arXiv:2306.10812 (2023)