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A statistical method based on the boson-mediated attraction in reciprocal space in metals is investigated. By partitioning electrons in k-pair states, each corresponding to a definite value of the attraction (energy contribution) and by a suitable counting of such microscopic states (entropy contribution), the free energy is evaluated and the conditions for an instability from the normal to the superconducting state are given. It is found that the critical state is related to the singularity of the interaction at a boson energy ± w around the Fermi surface and that the BCS result corresponds to a possible cut-off at the singularity. A generalisation of the BCS theory is discussed for the case when the cut-off is modified by damping of pairs. This accounts for high T(c)s and attenuation of the isotopic effect and predicts an increase, a decrease and a maximum of T(c) with carrier density in ceramic superconductors.

Additional information

Authors: MANES L, JRC Ispra (IT);DALLACASA V, University of Parma, Parma (IT)
Bibliographic Reference: Paper presented: Conférence Internationale Supraconductivité, Paris (FR), Nov. 23-24, 1989
Availability: Available from (1) as Paper EN 34917 ORA
Record Number: 199010801 / Last updated on: 1994-12-01
Original language: en
Available languages: en