"Nanoscale physics"

Properties of renormalized spectrum 
of interacting with polarization phonons localized quasiparticle with degenerated excited state 
М. Ткаch, Ju. Seti, О. Voitsekhivska, V. Gutiv, M. Ivanochko, E. Vereshko
Yuriy Fedkovych Chernivtsi National University, 2, Kotsyubinsky Str., 58012, Chernivtsi, Ukraine,
E-mail: j.seti@chnu.edu.ua
Modern nano-devices (quantum cascade lasers and detectors) contain the complicated elements which are the multi-layered structures consisting of many quantum wells and barriers. As a result, the degenerated states of localized quasiparticles (electrons and holes) interacting with polarization phonons are observed in such structures. It is clear that the renormalized spectrum in degenerated systems, depending on the parameters of intra- and interlevel interaction with phonons, essentially differ from that in non-degenerated systems in wide range of energies, containing the thresholds of radiation of several phonons.
In the proposed paper, using the recently developed theoretical method [1-3] in the approach of modified Feynman-Pines diagram technique at Т=0 К, the calculation of renormalized due to interaction with phonons spectrum of localized quasiparticle with initially degenerated level of two excited states is performed. It is established the splitting of main energy states and their phonon satellite bands depending on the initial distance to the main level. It is revealed the specific splitting of the groups of levels in resonant and non-resonant energy regions.

1.	Tkach M.V., Seti Ju.О., Voitsekhivska О.М. Diagram technique in method of Green’s functions for quasiparticles interacting with phonons. Chernivtsi : Chernivtsi National University named after Jurii Fedkovich. – 2019. – 162p.
2.	Tkach, M., Seti, J., Pytiuk, O., Voitsekhivska O. Renormalized spectrum of three-level localized quasiparticle interacting with polarization phonons at cryogenic temperature // J. Low Temp. Phys.– 2019. – 195. – P. 26 - 36.
3.	Tkach M.V., Pytiuk O.Yu., Voitsekhivska O.M., Seti Ju.O. Generalized method of Feynman-Pines diagram technique in the theory of energy spectrum of two-level quasiparticle renormalized due to multi-phonon processes at cryogenic temperature // Condensed Matter Physics. – 2018. – 21 – P. 43703.