Superconductivity in the pseudogap state induced by short-order fluctuations

Peculiarities of the superconducting state (s and d pairing) are considered in a simple model of the pseudogap state caused by short-range fluctuation s (e.g., of the antiferromagnetic type), which is based on the model of a F ermi surface with "hot" regions. A system of Gor'kov recurrence equations i s constructed taking into account all diagrams in perturbation theory in th e electron interaction with short-range fluctuations. The superconducting t ransition temperature is determined, and the temperature variation of the e nergy gap depending on the pseudogap width and the correlation length of sh ort-range fluctuations is analyzed. In a similar approximation, a microscop ic derivation of the Ginzburg-Landau expansion is carried out, and the beha vior of the main physical parameters of the superconductor near the transit ion temperature is studied depending on the pseudogap width as well as the correlation length of the fluctuations. The obtained results are in qualita tive agreement with a number of experiments with underdoped HTSC cuprates. (C) 2001 MAIK "Nauka/ Interperiodica".