ENERGY GAP, TRANSITION TEMPERATURE AND ELECTRON-ELECTRON INTERACTION OF WEAK COUPLING SUPERCONDUCTORS TIN AND INDIUM AS A FUNCTION OF MEAN FREE PATH OF ELECTRONS

The energy gap and the transition temperature of the weak coupling superconductors tin and indium are measured as a function of the mean free path of the electrons. Both of them increase with decreasing mean free path. The ratio α=2 Δ0/kTc increases proportionally to the reciprocal mean free path from 3.6 to 4.0 for tin and from 3.6 to 3.95 for indium. A theoretical consideration is presented showing that the electron-electron interaction is increased in dirty superconductors. Without any fit we find from the theoretical calculation an increase in NV for indium of δNV=5 · 10-10 m/ltr and for tin δNV=2 · 10-10 m/ltr (ltr is the transport mean free path of the electrons). The experiments give an increase in NV for indium of δNV=4.2 · 10-10 m/ltr and for tin δNV=1.7 · 10-10 m/ltr. The agreement is surprisingly good. © 1969 Springer-Verlag.