Fate of the Josephson effect in thin-film superconductors
Fate of the Josephson effect in thin-film superconductors
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DOI：
10.1038/nphys154
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发表时间：
2005-11-01
期刊：
影响因子：
19.6
通讯作者：
Goldbart, PM
中科院分区：
文献类型：
--
作者：
Hermele, M;Refael, G;Goldbart, PM
直流约瑟夫森效应指的是无耗散的电流，即可以通过连接两个大块超导体的弱链路持续传输的超电流。这一效应揭示了超导态的本质，而超导态的本质主要取决于空间维度。对于块状（即三维）超导体来说，超导性是最坚固的，即使在非零温度下，约瑟夫森效应也能持续。然而，在电线和薄膜中，热和量子波动起着至关重要的作用。在超导导线中，这些效应定性地改变了薄弱环节上的电传输。尽管有几个涉及薄膜超导体之间弱连接的实验，但很少有理论关注这种系统中的导电性。在这里，我们分析了两个超导薄膜通过点接触连接的情况。值得注意的是，约瑟夫森效应在非零温度下不存在。点接触电阻不为零，并随温度以近乎激活的方式变化，具有由表征薄膜的超流体刚度设置的通用能量势垒。这种行为反映了薄膜超导体的微妙性质，在未来的实验中应该可以观察到。
The d.c. Josephson effect refers to the dissipationless electrical current-the supercurrent-that can be sustained across a weak link connecting two bulk superconductors. This effect probes the nature of the superconducting state, which depends crucially on spatial dimensionality. For bulk (that is, three-dimensional) superconductors, the superconductivity is most robust and the Josephson effect is sustained even at non-zero temperature. However, in wires and thin films, thermal and quantum fluctuations play a crucial role. In superconducting wires, these effects qualitatively modify the electrical transport across a weak link. Despite several experiments involving weak links between thin-film superconductors, little theoretical attention has been paid to the electrical conduction in such systems. Here, we analyse the case of two superconducting thin films connected by a point contact. Remarkably, the Josephson effect is absent at non-zero temperature. The point-contact resistance is non-zero and varies with temperature in a nearly activated fashion, with a universal energy barrier set by the superfluid stiffness characterizing the films. This behaviour reflects the subtle nature of thin-film superconductors and should be observable in future experiments.