Resistive current states in wide superconducting films in zero magnetic field

Abstract

The temperature dependence of the current-voltage characteristics of high-quality thin films of tin from 7 to 50 µm thick are investigated in the absence of an external magnetic field. For the first time, we have experimentally observed phase slip centres (PSCs) and phase slip lines (PSLs) on the same superconducting tin film with known parameters in the temperature intervals corresponding to the mechanisms of their formation and existence. We have shown that the states of a wide film with increasing transport current appear in the following order: the superconducting state for current less than critical; the resistive vortex state for current more than critical, but less than maximum current for the uniform flux flow (instability current); the critical state due to the onset of instability of the steady pattern of viscous motion of the vortices; a vortex-free resistive state with PSLs for current more than instability current, but less than the upper critical current; and the normal state at a current higher than the upper critical current.

Phase-Slip Processes in Superconducting Films: AC Josephson Effect and New Phase Transition

“…At I = I m , the current density becomes equal to the critical one not only at the edges, where vortices are nucleated, but also in the middle of the film [2,3]. By the present investigation we confirm that at I > I m (T ) the resistive vortex state becomes unstable, and the wide film undergoes a jump-like transition to the new resistive state due to the appearance of a phase-slip line [1] already in the absence of a vortex structure.…”

“…The objects of the study were thin (d ξ(T ), λ ⊥ (T )) tin films prepared by the technique described in [1]. (Here ξ(T ) is the coherence length, λ ⊥ (T ) is magnetic field penetration depth into the film.)…”

Enhancement of critical current by microwave irradiation in wide superconducting films

“…As the temperature decreases, the film exhibits a crossover to an essentially inhomogeneous current state, in which vortex nucleation is responsible for the resistive transition; in what follows, this regime will be referred to as a wide film regime. A following quantitative criterion of such a crossover was formulated in [6] on the basis of careful measurements: if the temperature T satisfies an implicit condition w < 4λ ⊥ (T ), the superconducting film can be treated as a narrow channel, whereas at w > 4λ ⊥ (T ) it behaves as a wide film. The physical interpretation of this criterion is quite simple: existence of the resistive vortex state requires at least two opposite vortices (vortex and anti-vortex), with the diameter 2λ ⊥ each, to be placed across the film of the width w. At the same time, it was noted in [6] that after entering the wide film regime, the dependence I c (T ) ∝ (1 − T /T c ) 3/2 , typical for narrow channels, still holds within a rather wide temperature range, though the absolute value of I c is lower than the pair-breaking current I GL c (T ).…”

AC Josephson properties of phase slip lines in wide tin films

“…Indeed, the width of the sample used in [9] was 5 µm, whereas the penetration depth of the normal-to-film magnetic field λ ⊥ was 3-5 µm, i.e., close to the film width. As shown in [3], if the film width w does not exceed the quadrupled penetration depth, i.e., at w < 4λ ⊥ (T ), the transition of the superconducting film to the resistive phase slip state is similar to that in a narrow channel: it occurs as soon as the transport current approaches the value of the Ginzburg-Landau depairing current, bypassing the stage of the moving vortex lattice. Hence, strictly speaking, the experimental data in [9] were obtained for a narrow superconducting channel rather than for a really wide film.…”

“…Following the results of theoretical [10] and experimental [3] investigations of the stability of the vortex state in wide films, we assume the absence of moving vortices in the phase slip state of the samples.…”