A NEW CRITERION FOR A BULK TYPE-I OR TYPE-II SUPERCONDUCTOR

A new criterion for a bulk type I or type II superconductor is found by solving the first Landau-Ginsburg(LG) equation, including the cubic term. The functions obtained for the upper or lower critical field H (parallel or perpendicular to the surface of a sample) near Tc are: B= Dt′w 2±w D2t′2 4+D 3 2t′ 3 2 ky with t′=1- T Tc, w= n 2e, and B = μoH; D is an undetermined constant, ky is the equivalent wave number near Tc. When ky ≥ 0, it is a type I superconductor. When ky < 0, it is a type II superconductor. A similar criterion for a tin superconductor is also obtained. The agreement between the theory and experimental results is quite good. © 1990.