Upper critical field of borocarbide superconductors

We have investigated the upper critical fields of Y/sub 1-x/Er/sub x/Ni/sub 2/B/sub 2/C and Y/sub 1-x/Er/sub x/Pd/sub 5/B/sub 3/C/sub 0.4/ (0/spl les/x/spl les/1) systems by the scaling analysis of the thermal fluctuation conductivity. The experiments were done over wide magnetic field range. We are going to test the thermal fluctuation theory in the borocarbide superconducting systems. According to the scaling analysis, the thermal fluctuation conductivity should be scaled as /spl sigma//sub f/=((T2)/H)(1/3)F[A(T-Tc(H))/((TH)(2/3))]. Because the scaling function is field independent, all scaling curves obtained under various applied fields should converge to a universal curve if the function of T/sub c/(H) is properly chosen, We therefore obtain H/sub c2/(T) determined by optimizing the scaling fit. The superconducting coherence length and Ginzburg-Landau parameter K in those superconductors are also estimated. We categorize the Y/sub 1-x/Er/sub x/Ni/sub 2/B/sub 2/C and Y/sub 1-x/Er/sub x/Pd/sub 5/B/sub 3/C/sub 0.4/ systems as strong type-II superconductors.