Critical currents approaching the depairing limit at a twin boundary in YBa2Cu3O7−δ
Critical currents approaching the depairing limit at a twin boundary in YBa2Cu3O7−δ
复制标题
YBa2Cu3O7−δ 孪晶边界处的临界电流接近脱配对极限
作者：
I. Maggio;C. Renner;A. Erb;E. Walker;Ø. Fischer
自从高温超导体被发现以来，人们对涡旋物质的兴趣大大增加，高温超导体呈现出特别丰富和复杂的磁涡旋态。人们对近乎完美晶体中磁涡旋的整体行为——比如涡旋晶格的熔化——进行了大量研究，但从技术角度来看，更具相关性的是大多数实用超导体中存在的各种结构缺陷对涡旋态的影响。这类缺陷的一个重要例子是YBa₂Cu₃O₇₋₆（YBCO）孪晶正交晶体中的孪晶界。利用对磁场敏感的探测器对这类样品进行的研究表明，孪晶界在钉扎涡旋方面起着重要作用，从而提高了YBCO在保持超导的同时能够承载的电流。但是这些技术的空间分辨率较低，无法在涡旋或边界本身的尺度上研究这些效应。扫描隧道谱为规避这些分辨率问题提供了一种手段，因为它可以在纳米尺度上直接探测超导序参量。在此我们利用这种技术来研究YBCO中孪晶界的重要性。特别是，我们观察到垂直于边界的涡旋通量具有出乎意料的大钉扎强度，这意味着沿边界能够承载的临界电流接近理论上的“退耦合”极限。
Interest in vortex matter has risen considerably since the discovery of the high-temperature superconductors, which exhibit magnetic vortex states that are especially rich and complex. The global behaviour of magnetic vortices in nearly perfect crystals—such as melting of the vortex lattice—has been much studied, but of more technological relevance is the influence on the vortex states of the various structural defects present in most practical superconductors. An important example of such a defect is the twin boundary present in twinned orthorhombic crystals of YBa2Cu3O7−δ (YBCO). Studies of such samples using magnetic-field-sensitive probes have suggested that the twin boundary plays an important role in pinning the vortices and so enhancing the currents that YBCO can support while remaining superconducting. But the low spatial resolution of these techniques does not permit these effects to be studied at the scale of the vortices or boundaries themselves. Scanning tunnelling spectroscopy offers a means of circumventing these problems of resolution, as it directly probes the superconducting order parameter at nanometre length scales. Here we use this technique to investigate the importance of twin boundaries in YBCO. In particular, we observe an unexpectedly large pinning strength for perpendicular vortex flux across the boundary, which implies that the critical current that can be supported along the boundary approaches the theoretical ‘depairing’ limit.