Critical currents, phase slip centers, and phase slip lines in superconducting films in the absence of external magnetic field

Abstract

The temperature dependence of the current–voltage characteristics of high-quality thin films of tin from 7 to 50 μm thick is investigated in the absence of external magnetic field. For the first time on the same samples phase slip centers are observed near Tc, where the films are narrow channels, and phase slip lines are observed at lower temperatures, where the films become wide. The critical current exhibits temperature crossover, which affects its absolute value, but in a certain temperature interval a temperature dependence of the form (1−T/Tc)3/2 is maintained. When the temperature is decreased further, the critical current at which vortices due to the self-field of the current can enter the sample depends linearly on temperature and corresponds to the Aslamazov–Lempitsky theory. The temperature at the start of crossover with decreasing temperature coincides with the temperature at which the film width is equal to four times the penetration depth of a weak magnetic field perpendicular to the film plane. On one side of this equality the films are narrow, and on the other side they are wide. The current at which the first phase slip center forms is the Ginzburg–Landau critical current for pair-breaking, distributed uniformly over the width of the film. The current of formation of the first phase slip line is the current of vortex-state instability predicted by Aslamazov and Lempitsky, which is distributed over the width of the film in a specific way.