Effect of inhomogeneous coupling on BCS superconductors
Abstract
We investigate the influence of inhomogeneity in the pairing coupling constant U(r⃗) on dirty BCS superconductors, focusing on Tc , the order parameter Δ(r⃗) , and the energy gap Eg(r⃗) . Within mean-field theory, we find that when the length scale of the inhomogeneity is comparable to or larger than the coherence length, the ratio 2Eg/Tc is significantly reduced from that of a homogeneous superconductor, while in the opposite limit, this ratio stays unmodified. In two dimensions, when strong phase fluctuations are included, the Kosterlitz-Thouless temperature TKT is also studied. We find that when the inhomogeneity length scale is much larger than the coherence length, 2Eg/TKT can be larger than the usual BCS value. We use our results to qualitatively explain recent experimental observation of a surprisingly low value of 2Eg/Tc in thin films.
- Publication:
-
Physical Review B
- Pub Date:
- April 2008
- DOI:
- 10.1103/PhysRevB.77.144523
- arXiv:
- arXiv:0712.1761
- Bibcode:
- 2008PhRvB..77n4523Z
- Keywords:
-
- 74.78.-w;
- 74.20.-z;
- 74.81.-g;
- Superconducting films and low-dimensional structures;
- Theories and models of superconducting state;
- Inhomogeneous superconductors and superconducting systems;
- Condensed Matter - Superconductivity
- E-Print:
- 12 pages, 14 figures