Effect of magnetic-field-induced frustration on the superconducting transition of proximity-coupled arrays

The magnetic field dependence of the superconducting transition has been studied in triangular arrays of Pb-Sn proximity-coupled junctions. The transition temperature Tc and the array resistance $R(T)$ are found to vary periodically in a perpendicular magnetic field with a period corresponding to one flux quantum per unit cell of the array. In addition, both quantities show substructure at rational fractions of a flux quantum f=ΦΦ₀=1/4,1/3,1/2,2/3,3/4. The current-voltage characteristics of the arrays are nonlinear at temperatures near the transition temperature Tc, with voltage increasing as a power of the current V~Ia(T,f). As a function of reduced temperature t=[Tc(f)-T]Tc(f), the power-law exponent $a(t,f)$ is insensitive to f.