Nonextensive thermodynamics applied to superconductivity

We have shown that the weak-coupling limit superconductors are well described by qsimilar to1, where q is a real parameter which characterizes the degree of nonextensivity of Tsallis' entropy. Nevertheless, small deviations with respect to q=1 provide better agreement when compared with experimental results. We have also shown that the generalized BCS theory with q>1 exhibit power-law behavior of several measurable macroscopic functions in the low-temperature regime. These power-law properties are found in many high-T-c oxides superconductors and motivated us to extend Tsallis' entropy calculations to these systems. Therefore. we have calculated the phase diagram and the specific heat and we compare our results with the experimental data for the YBa2Cu3O7-delta family of compounds. (C) 2002 Elsevier Science B.V. All rights reserved.