Superconducting glass with diagonal disorder

A model of the superconducting transition in a system with localized negative U pairing centers is studied in the limit U≫t (t is the width of the conduction band): the superconducting glass model. The critical temperature depends nonexponentially on the magnitude of the interaction U. However, the final expressions for the thermodynamic quantities presented differ little from the predictions of the standard BCS theory of superconductivity. A value of 2Δ0/Tc exceeding 4 is obtained and depends weakly on the electron concentration. The effect of diagonal disorder (spread in site energies) on the magnitude of Tc and the behavior of the system near the percolation threshold are examined. In contrast to the BCS model, the model of superconducting glass is extremely sensitive to the structural state of the lattice. The tunnel effect in superconducting glasses is examined and the accessible experimental information is discussed.

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