Low Temperature Physics: 35, 169 (2009); https://doi.org/10.1063/1.3081150 (29 pages)
Fizika Nizkikh Temperatur: Volume 35, Number 3 (March 2009), p. 227-264    ( to contents , go back )

Fluctuation conductivity and pseudogap in high-temperature YBCO superconductors

A.L. Solovjov1 and V.M. Dmitriev1,2

1B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Lenin Ave., Kharkov 61103, Ukraine
E-mail: solovjov@ilt.kharkov.ua

2International Laboratory of High Magnetic Fields and Low Temperatures, 95 Gajowicka Str., 53-421 Wroclaw, Poland

Received Octouber 10, 2008

Abstract

Some theoretical and experimental papers reflecting the current status of investigation of high temperature superconductivity and such an unusual phenomenon as a pseudogap in high-Tc superconductors (HTSC) are reviewed. The concept of local pairs in systems with low and intermediate density of current carriers (among these are HTSC) is considered. The experimental part is mainly based on the study of excess fluctuation conductivity (FC) in thin epitaxial films of YВа2Сu3O7-y (YBCO) and Y1-xРrxВа2Сu3O7-y (YPrBCO). Proposed and experimentally justified is a new approach to the analysis of FC and pseudogap in such high-Tc systems. The approach is based on the assumption that in HTSC at temperatures well above Tc the excess conductivity σ′(T) appears as a result of the formation of paired states in the form of noninteracting strongly coupled bosones. As the temperature is decreased, these occurs a crossover from the regime of local pairs which obey the theory of Bose-Einstain condensation to a regime of fluctuating Cooper pairs following the BCS theory.

PACS: 71.27.+a Strongly correlated electron systems;
PACS: 74.76.Bz High-temperature superconductor films;
PACS: 74.40.+k Fluctuation superconductivity.

Key words: high-temperature superconductivity, fluctuation superconductivity, pseudogap, local pairs, Bose-Einstain condensation.

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