When: March 05, 16:00
Where: Skoltech, MR-408 (TROC-3, Blue building)
The theory of Coulomb complexes in semiconductors and nanosystems
Dr. Marina Semina
Ioffe Institute, St.-Petersburg, Russia
The seminar is devoted to review of the recent theoretical results on excitons and trions in Van der Waals heterostructures based on transitional metal dichalcogenides monolayers and Rydberg excitons in bulk Cu2O crystals.
The exciton is a hydrogen-like complex consisting of electron and hole pair bound by Coulomb interaction, trions are three-particle complexes consisting of electron (hole) bound to exciton. Although the hydrogen-like model has proved itself to be very adequate to describe excitons, in real world even not localized excitons demonstrate the difference from hydrogen-like model related, for example, to particular features of the dielectric environment or to the band structure and crystal anisotropy.
The dielectric environment leads to the strong difference of the interaction between charge carriers from the Coulomb one in transitional metal dichalcogenides monolayers. The effective interaction potential is much weaker in small distances than Coulomb one. As a result, the exciton series strongly differs from the 2D Rydberg series. In the talk the results on exciton and trion in one and two layer Van der Waals heterostructures will be presented: binding energies of exciton and trions, fine structure of the trions in WSe2 and WS2. As Van der Waals heterostructures consists of several layers the interference effects have important contribution to their optical spectra, which makes possible to vary exciton radiative lifetime almost by an order of magnitude.
The Cu2O is the first material where the Wannier-Mott excitons were observes. The interest to that system returned after observation the series of 25 excitonic states by M. Bayer group in TU Dortmund in 2014. These highly excited states have a size up to micrometer and can be considered as macroscopic quantum objects. After that the series of experiments were carried out and the theory of Rydberg excitons (including effects of external fields) was needed. In the talk the following results will be presented: the description of excitons fine structure in zero field case (the appearance of the states with high orbital momentum and their fine structure), the scaling of the exciton parameters with the principal quantum number, the quantitative description of Stark effect and exciton dissociation in external electric field.
All presented results will be illustrated by experiments made by X. Marie group (INSA, Toulouse) and M. Bayer group (TU Dortmund)
1999-2005 student at Peter the Great St. Petersburg Polytechnic University
from 2005 works at Ioffe Institute (now senior researcher)
2005-2009 PhD under Proffessor Robert Suris
19 may 2009 PhD thesis defense at Ioffe Institute
2009 and 2018 the prize at the competition for best series of scientific works at Ioffe Institute