LONDON PENETRATION DEPTH OF STRONGLY COUPLED ISOTROPIC SUPERCONDUCTORS - LOW-TEMPERATURE BEHAVIOR

We proceed to a systematic exploration of the low-temperature dependen ce of the London penetration depth of isotropic superconductors within strong-coupling theory in the clean limit. For a sizable range of par ameters, we find that strong-coupling effects can reasonably simulate a pourer law dependence, sometimes with excellent precision. In such c ases ii would be quite difficult to distinguish experimentally between a pure power law and the strong-coupling: result. Physically we have been able to ascribe this temperature dependence to low-frequency phon ons which produce a quasielastic scattering for electrons. The presenc e of these low-frequency phonons requires rather wide phonon spectra a nd their effectiveness In scattering implies a fairly strong coupling.