Physics – Condensed Matter – Superconductivity
Scientific paper
2007-12-11
Phys. Rev. B 77, 144523 (2008)
Physics
Condensed Matter
Superconductivity
12 pages, 14 figures
Scientific paper
10.1103/PhysRevB.77.144523
We investigate the influence of inhomogeneity in the pairing coupling constant $U(\vec r)$ on dirty BCS superconductors, focusing on $T_c$, the order parameter $\Delta(\vec r)$, and the energy gap $E_g(\vec r)$. 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 $2E_g/T_c$ 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 $T_{KT}$ is also studied. We find that when the inhomogeneity length scale is much larger than the coherence length, $2E_g/T_{KT}$ can be larger than the usual BCS value. We use our results to qualitatively explain recent experimental observation of a surprisingly low value of $2E_g/T_c$ in thin films.
Klich Israel
Refael Gil
Zou Yue
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