Superconducting current in hybrid heterojunctions of metal-oxide superconductors: Size and frequency dependencesстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:We have detected experimentally considerable deviations of the frequency dependences of the Shapiro step amplitudes and the critical current of Nb/Au/YBa2Cu3Ox thin-film hybrid Josephson heterojunctions prepared on YBa2Cu3Ox metal-oxide superconductor films with a tilted c axis from the regularities inherent in Josephson junctions of traditional superconductors with an s-symmetry of the order parameter. It is shown that possible formation of "splintered" fluxons with a size lambda(s) < lambda(J) due to faceting of the interface and formation of a chain of nanosize 0 and pi junctions must be taken into account in describing processes in lumped heterojunctions (whose size L is smaller than the Josephson penetration depth lambda(J) determined from the averaged value of the critical current density). For heterojunctions with a size lambda(s) < L < lambda(J) , a substantial decrease in the maximal amplitude of the first Shapiro step with increasing voltage (Josephson oscillation frequency) is observed at voltages much smaller than the energy gap in niobium (V << Delta(Nb)/e); this effect is manifested most strongly when the size L is greater than lambda(s). A fractional Shapiro step and a subharmonic detector response have been observed in the current-voltage characteristics of heterojunctions; the dynamic processes responsible for their emergence and indicating the presence of the second harmonic in the current-phase relation are studied. It is shown that the effect of interface faceting on the current-phase relation increases with a heterojunction size L > lambda(s). (c) 2005 Pleiades Publishing, Inc.