Influence of microwave irradiation on the dc resistive state of a wide superconducting film

Abstract

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.

Effect of meter-range electromagnetic irradiation on the current-voltage characteristics of wide superconducting films

“…1b, under the action of microwave irradiation ( f = 5.56 GHz), the film resistivity, caused by the motion of the vortices (a small initial linear part of the IVC No. 1), decreases and then disappears at a certain power level, in accordance with earlier results [13]; simulaneously, the current I m of occurrence of the first PSL decreases and finally turns to zero.…”

“…As seen in Fig.1b, under the action of microwave irradiation ( f = 5.56 GHz), the film resistivity, caused by the motion of the vortices (a small initial linear part of the IVC No. 1), decreases and then disappears at a certain power level, in accordance with earlier results[13]; simulaneously, the current I m of occurrence of the first PSL decreases and finally turns to zero.The effect of an alternating field of the rf band ( f = 35.5 MHz, Fig.1a) is radically different: the critical current I c decreases significantly faster with increasing power than I m . As a result, the initial part of the IVC considerably extends, its slope increases, and most of this part remains linear.…”

“…A possible cause of the disappearance of the vortex resistivity may be rapid oscillatory motion of the vortices caused by the microwave current with a small period. This prevents formation of new vortices at the edges of the film, which, according to [5], requires much longer time of the order of τ ∆ (see a detailed discussion in [13]).…”

“…Among the possible reasons for these differences, we first of all mention the insufficiently low frequency of irradiation (in the experiment, the relaxation parameter value ωτ ∆ ≈ 0.9 most likely corresponds to the transition regime to the adiabatic limit ωτ ∆ ≪ 1), as well as the existence of other characteristic times of the system. For example, the vortex flight time τ across the film, according to estimates in [13], may exceed τ ∆ by an order of magnitude and even more. Since the adiabaticity condition for this time, ωτ ∆ ≪ 1, is not satisfied in our experiment, the assumption of a locally steady state may be violated, therefore the quantitative applicability of the model requires usage of a lower-frequency radiation.…”

“…For instance, when studying the rf field absorption by the vortices in Pb 0.83 In 0.17 and Nb 0.95 Ta 0.05 films with a large number of pinning centers [12], it was found that the alternating field of certain frequencies above 3.9 − 15 MHz causes the appearance of vortex resistivity and the corresponding increase in the absorbed power due to depinning of vortices. However, in our early studies of the effect of the microwave field (1-15 GHz) on the vortex resistive state in the films with a small number of defects [13], the opposite effect compared to [12] was found: suppression of the vortex resistivity by the electromagnetic field. It was shown that with increasing microwave power P, the resistive vortex part of the IVC decreases and completely disappears at P ≥ 0.4P c (P c is the power at which the critical current vanishes).…”