Title: Renormalized energy of ground and first excited state of Fröhlich polaron in the range of weak coupling
Author(s):

	M.V. Tkach (Chernivtsi National University, 2 Kotsyubinsky St., 58012 Chernivtsi, Ukraine) ,
	Ju.O. Seti (Chernivtsi National University, 2 Kotsyubinsky St., 58012 Chernivtsi, Ukraine) ,
	O.M. Voitsekhivska (Chernivtsi National University, 2 Kotsyubinsky St., 58012 Chernivtsi, Ukraine) ,
	O.Yu. Pytiuk (Chernivtsi National University, 2 Kotsyubinsky St., 58012 Chernivtsi, Ukraine)

The partial summing of infinite range of diagrams for the two-phonon mass operator of polaron described by Frohlich Hamiltonian is performed using the Feynman-Pines diagram technique. The renormalized spectral parameters of ground and first excited (phonon repeat) polaron state are accurately calculated for the weak electron-phonon coupling at T=0 K. It is shown that the stronger electron-phonon interaction shifts the energy of both states into low-energy region of the spectra. The ground state stays stationary and the excited one - decays at bigger coupling constant.

Key words: polaron, phonon, electron-phonon interaction, Green's function, mass operator
PACS: 71.38.-k, 63.20.kd, 63.20.dk, 72.10.Di

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