The current-voltage characteristics of high-quality thin tin films, ranging in width from 7 to 50 μm, irradiated by microwave radiation are investigated. The behavior of the critical current Ic and of the maximum current Im for the existence of a stationary flow of the characteristic vortices of the transport current (formation current of the first phase-slip line) is analyzed. The regimes of enhancement and suppression of the currents Ic and Im by a microwave field are studied and analyzed. The criteria for separating films into narrow and wide are established. It is shown that the superconductivity enhancement effect is a general effect and is observed for uniform (narrow films) and nonuniform (wide films) distributions of the superconducting current over the film width.

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.

The influence of a microwave field on the resistive state brought on in a wide film by the passage of a dc current is investigated experimentally. In this situation the resistivity arises as a consequence of two processes: the motion of Pearl–Abrikosov vortices of the self-magnetic field of the current, and phase slip of the superconducting order parameter. It is shown that under microwave irradiation the resistivity of the film due to the vortex mechanism decreases, and at high power levels (P>0.4Pc) it vanishes, and then the resistivity of the film is due solely to phase slip processes, as in narrow vortex-free channels. It is found experimentally that, starting at some power level P*<Pc, the electromagnetic field plays a governing role in the processes giving rise to phase-slip lines. A similar conclusion is reached from a study of the influence of a microwave field on the differential resistance of a phase-slip center in narrow vortex-free channels; this suggests that phase-slip processes in wide and narrow films share a common nature.