Off-Diagonal Nonmagnetic Disorder in s- and d-Wave Superconductors

Abstract

The previously developed approach to study off-diagonal disorder has been extended and applied to both s-and d-wave superconductors. The derived equations allow the self-consistent solution of the problem. For a special case of negative U centres embedded in non-superconducting host we have calculated their critical concentration for the appearance of superconductivity and found it equal to ≈ 0.4. For x > x cr the order parameter continuously increases to its maximal value at x = 1.

A real space approach to study the effect of off-diagonal disorder on superconductivity

“…The DOS at the band centre becomes non-zero even with the introduction of a slightest amount of disorder. This observation agrees with earlier CPA studies [18,19]. But unlike diagonal disorder parameter D, change in off-diagonal disorder parameter d does not affect the pseudo-gap in the DOS appreciably (see Fig.…”

“…Unless simplified assumptions are made about off-diagonal disorder [17], the single-site CPA cannot deal with problems involving correlated randomness involving more than one site. The only mean-field work which included the effect of off-diagonal disorder in superconductivity was by Michalik and Wysokiń ski [18,19] who used a version of the CPA proposed by Blackman et al [20] to incorporate off-diagonal disorder. We emphasize here that it is in the ability to treat off-diagonal disorder that the real strength of the ASF becomes particularly evident and will be clear from the discussions of the present paper.…”