Method of successive separation and summing of multiplicative diagrams of mass operator for the multi-level quasiparticle interacting with polarization phonons

• Published in: Condensed Matter Physics
• Main Authors: M.V. Tkach, Ju.O. Seti, O.M. Voitsekhivska, V.V. Gutiv
• Format: Article
• Language: English
• Published: Yukhnovskii Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine 2019-09-01
• Subjects: diagram technique; quasiparticle; mass operator; phonon; spectrum
• Online Access: https://doi.org/10.5488/CMP.22.33703

The theory of renormalized energy spectrum of a multi-level quasiparticle interacting with polarization phonons at T = 0 K is developed within the Feynman-Pines diagram technique in a new approach. It permits a successive separation of multiplicative diagrams from non-multiplicative ones for all orders of mass operator, and their partial summing as well. The obtained mass operator is presented as a sum of branched chain fractions, which effectively take into account the multi-phonon processes. For the two-level quasiparticle it is shown that just the interlevel (non-diagonal) interaction with phonons fundamentally changes the properties of the spectrum. In the vicinity of all threshold energies, the quasi-equidistant phonon satellite bands (i.e., groups of energy levels) are formed. They correspond to the complexes of bound states of a quasi-particle with many phonons.