Seminar usually takes place on Fridays at 13:10 in lecture room A 1032 on 10th floor in Trója, V Holešovičkách 2, Praha 8
Future seminars:
November 7, 2025
Spectrum of excitons in 2D semiconductors
Artur Slobodeniuk
Dept. of Condensed Matter Physics, MFF UK
Coulomb interaction in a non-uniform dielectric medium is one of the central topics in the study of a wide range of nanoscale materials, such as graphene, atomically thin crystals, and their heterostructures. In recent years, this problem has been extensively discussed in the context of exciton investigations in monolayers of semiconducting transition metal dichalcogenides (S-TMDs).
In particular, it has been found that the spectrum of s-type excitonic states in these 2D semiconductors does not follow the Rydberg series of the idealized 2D hydrogen atom model. The primary reason for this deviation is the dielectric inhomogeneity of S-TMD structures, which modifies the Coulomb interaction between the electron and hole in the exciton.
A common approach to account for the excitonic spectra of S-TMD monolayers involves numerical solutions of the Schrödinger equation, where the electron-hole attraction is approximated by the Rytova-Keldysh potential. However, such numerical solutions do not shed light on the general structure of the excitonic spectrum as a function of the system parameters.
In this work, we propose an alternative approach that enables the derivation of (semi)analytical expressions for the exciton spectrum and offers insights into their other electrodynamical properties. The obtained expression for the exciton spectrum has been validated in several cases of S-TMD monolayers and has been used to extract excitonic characteristics of MoSe2, WS2, and MoS2 monolayers encapsulated between hexagonal boron nitride flakes, based on spectroscopic data.
November 14, 2025
Atom induced coupling between first and third QED radiation modes
Petra Ruth Kaprálová
Dept. of radiation and chemical physics, Institute of Physics AVCR
The present work concerns research of methods for efficient conversion of light between the well accessible infrared radiation into shorter wavelengths using interaction with matter. The currently used process, high harmonic generation, allows conversion up to X-rays, nevertheless its efficiency is very low. The light is emitted due to a semiclassical recollision mechanism. In contrast, I will talk about an inherently quantum mechanism which would be based on the use of resonantly excited atomic transitions. I will present a new type of resonant transition involving two bound atomic states and ionization continuum and prove the coherent superposition of these states with radiation modes. Finally, I will explain my prediction of strong third harmonic generation within the framework of classical and quantum electrodynamics.
Past seminars:
September 10, 2025 (double seminar)
Experimental attosecond physics in the gas phase.
Maximilian Forster
TUM, Garching
Photoemission Timing on Metal Surfaces.
Sven-Joachim Paul
TUM, Garching
October 24, 2025
Approximations in calculation of inelastic electron molecule collisions.
Martin Cizek
ITF, MFF UK
Informal seminar for students on the nonlocal discrete-state-in-continuum theory of inelastic electron molecule collisions and various approximations used.