LOW-TEMPERATURE PENETRATION DEPTH OF STRONGLY COUPLED SUPERCONDUCTORS

We have made in the clean limit a systematic exploration within strong coupling theory of the low temperature dependence of the London penet ration depth for isotropic superconductors. We have found that strong coupling effects can reasonably simulate a power law dependence for an important range of parameters characterizing the boson spectrum respo nsible for pairing. Sometimes the precision is excellent. In such case s it would be quite difficult to distinguish experimentally between a pure power law and the strong coupling result. The physical origin of this temperature dependence is the quasi elastic scattering of electro ns by low frequency bosons. Rather wide boson spectra are required in order to have these low frequency bosons at low temperature and a fair ly strong coupling is necessary for their scattering to be effective.