Title: Continuous unitary transformation approach to pairing interactions in statistical physics
Author(s):

T.Domański (Institute of Physics, M. Curie Skłodowska University, 20-031 Lublin, Poland)

We apply the flow equation method to the study of the fermion systems with pairing interactions which lead to the BCS instability signalled by the appearance of the off-diagonal order parameter. For this purpose we rederive the continuous Bogoliubov transformation in a fashion of renormalization group procedure where the low and high energy sectors are treated subsequently. We further generalize this procedure to the case of fermions interacting with the discrete boson mode. Andreev-type interactions are responsible for developing a gap in the excitation spectrum. However, the long-range coherence is destroyed due to strong quantum fluctuations.

Key words: continuous unitary transformation, pairing interactions, superconductivity
PACS: 05.10.Cc, 74.20.Fg, 71.10.Li