Upper Critical Fields of Amorphous Bi and Bi-Pb Alloys

The previously measured Hc2(T)in amorphous pure Bi,Bi75Pb25,BisoPbso and Bi30Pb70 showed the upward deviation from the dirty limit values predicted by the Werthamer-Helfand-Hohenberg theory. The strong coupling effect was taken into account at that time for this enhancement of Hc2(T), but it has recently been shown that the distribution of electrical diffusivity might be important and intrinsic in these metastable phases. Our experimental results are reexamined on the basis of this model,that is,the enhancement of Hc2(T)is caused by the inhomogeneous spatial distribution of electrical diffusivity. It is found that the amorphous Bi-Pb system has the similar distribution of electrical diffusivity,while the amorphous pure Bi has a different one.