Coherence length in superconductors from weak to strong coupling

Abstract

We investigate the evolution of the superconducting coherence length ξ0 from weak to strong coupling, within both an s-wave and a d-wave lattice model. We show that the identification of ξ0 with the Cooper-pair size ξpair in the weak-coupling regime is meaningful only for a fully gapped (e.g., s-wave) superconductor. Instead in a d-wave superconductor, where ξpair diverges, we show that ξ0 is finite (and of the expected order of magnitude) when properly defined as the characteristic length scale for the correlation function of the amplitude of the superconducting order parameter. The strong-coupling regime is quite intriguing, since the interplay between the particle-particle and the particle-hole channel is no more negligible. In the case of s-wave pairing, which allows for an analytical treatment, we show that ξ0 is of the order of the lattice spacing at finite densities. In the diluted regime ξ0 diverges, recovering the behavior of the coherence length of an effective bosonic system. Similar results are expected to hold for d-wave superconductors. We also comment on the consequences of our results with respect to the physics of high-Tc superconducting cuprates.

Source-reported materials — not catalogue approval

Similar papers