CRITICAL-TEMPERATURE OF ANISOTROPIC SUPERCONDUCTORS FROM ELIASHBERG THEORY

We consider the general problem of finding the critical temperature of anisotropic superconductors from Eliashberg equations. Our study is valid for any spectral shape and any anisotropy. We solve this problem in the strong coupling limit and show that in this case the gap (at T(c)) is isotropic. Therefore strong coupling in anisotropic superconductors tends to produce isotropic gaps. We solve also the problem in the weak coupling limit by generalizing a preceding approach for isotropic superconductors. In the intermediate regime we propose a formula which interpolates smoothly between weak and strong coupling.