Stimulation of critical current and vortices movement in wide microbridges based on epitaxial YBCO films

Abstract

Wide microbridges made of epitaxial YBCO films were investigated experimentally both under and without 37 GHz microwave irradiation at T=4.2 K. Under weak irradiation enhancement of critical current was observed. Current steps in the I-V characteristics caused by synchronization of Abrikosov vortices flow in microwave field were also found, while in the absence of irradiation the microbridges displayed no Josephson properties.

Quasi-Josephson effects generated by coherent vortex flow in easy motion laser processed channels

“…2 shows I-V of double channel LW bridge irradiated with 1.25 GHz microwave power at T = 67.5 K. The distance between clearly pronounced current steps changes with changing frequency of microwave radiation following the Josephson frequency-voltage relationship. The height of the zero order step, see the inset, decreases with increasing microwave power, as predicted for the QJE [2].…”

“…[2,3] The voltage distance between consecutive steps is 0921-4534/$ -see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2010.02.005 constant and given by the Josephson relation DV = hf/2e.…”

“…doi:10.1016/j.physc.2010.02.005 constant and given by the Josephson relation DV = hf/2e. The zero order QJE step (critical current) is expected to decrease linearly with increasing microwave power [2]. It is known that QJE can cause the appearance of current steps on I-V curves even in the absence of any external radiation in the conditions of highly coherent vortex motion.…”

The critical parameters enhanced by microwave field in thin-film type-II superconductors

“…With a further increase in power of microwave irradiation the critical superconducting current decreases, and harmonic and sub-harmonic steps of the current appear at voltages on the bridge V m,n related to the frequency of an external electromagnetic field f by the Josephson relation: V mn = (n/m)hf /2e, where m, n are integers, h is Planck's constant, e is the electron charge. The authors of reference [4] suggest that the mechanism responsible for the increase of I c and I s in the investigated bridges of HTSC is an energy diffusion of quasiparticles in a contact area caused by a "jitter" of the potential well due to microwave irradiation [2]. It is this mechanism of enhancement of superconductivity that was also found in cuprate HTSC by other experimenters.…”

“…After the discovery of high-temperature cuprate superconductors (HTSC), which caused an increased research activity, there has been a series of works devoted to the experimental study of an effect of microwave irradiation on the superconducting properties of HTSC films. Reference [4] was among the first which mentioned the finding of the effect of superconductivity enhancement in HTSC films. That paper shows a family of I-V characteristics (IVC) for wide (w∼ 10 µm) and long (L∼ 15 µm) bridge of an epitaxial film of Y Ba 2 Cu 3 O 7−x .…”