Superconducting spin currents

在几乎所有的超导体中，携带电荷的电子对都处于所谓的单重态，即两个电子的量子自旋是反平行的。无论材料是高温氧化物超导体，在这种情况下，配对对称性被描述为d波，还是传统的具有S波配对的金属超导体，都是如此。只有几种已知的化合物显示出所谓的p波超导电性，在这种超导中，一对电子的自旋是平行的，因此处于“三重态”。在过去的五年里，越来越多的证据表明，单态超导体和铁磁体之间的近距离耦合有时会在铁磁体内产生三态对--证据是，超导电流可以在长度尺度上通过铁磁材料，而这种长度尺度对于单态超导体来说太大了，以至于无法存活。今年早些时候，与另外两个国际组织一起，我们在展示如何以受控的方式创建这个三胞胎国家方面取得了突破。总而言之，这些结果为丰富的三重态超导新领域开辟了道路，在这个领域中，超流携带自旋的潜在能力可以与标准自旋电子学(自旋电子学)结盟。在这个项目中，剑桥大学的实验团队将与布里斯托尔的凝聚态物质理论小组发展现有的合作，以巩固他们在该领域的领先地位，并探索如何通过设备中的磁性元素来控制三重态电流，以便可以直接测量自旋超流。除了展示超导自旋电子器件，该项目还旨在研究通过利用预计具有良好的p波耦合但本身不是超导体的材料来创造人造p波超导体的潜力。该计划的结果将不可避免地刺激更广泛的科学界对非常规超导和自旋电子学感兴趣。我们相信，通过建立产生和控制自旋超流的基本过程，这项工作将为探索这一新现象的重要新的研究方向铺平道路。

In almost all superconductors the pairs of electrons which carry the charge are in the so-called "singlet" state in which the quantum spin of the two electrons is anti-parallel. This is true whether the materials are high temperature oxide superconductors in which case the pairing symmetry is described as d-wave, or conventional metallic superconductors which have s-wave pairing. There are only a few known compounds which show so-called p-wave superconductivity in which the electron spins within a pair are parallel and hence in a "triplet" state.During the past five years there has been increasing evidence that proximity coupling between singlet superconductors and ferromagnets can sometimes generate triplet pairs within the ferromagnet - the evidence being that supercurrents can be passed through ferromagnetic materials over length scales which are simply too large for singlet pairs to survive. Earlier this year, in parallel with two other international groups, we made a breakthrough in demonstrating how this triplet state can be created in a controlled way. Together, the results have opened the way for a rich new field of triplet superconductivity in which the potential ability of a supercurrent to carry spin can be allied with standard spin electronics ("spintronics").In this project the experimental team at Cambridge will develop an existing collaboration with the Condensed Matter Theory Group at Bristol to cement their lead in this field and to explore how triplet currents can be controlled by magnetic elements within a device so that the spin supercurrent can be directly measured. As well as demonstrating superconducting spintronic devices, this project also aims to investigate the potential of creating artificial p-wave superconductors by exploiting materials which are predicted to have a favourable p-wave coupling but which are not themselves superconductors. The results from this programme will inevitably stimulate the broader scientific community interested in unconventional superconductivity and spintronics. We believe that, by establishing the fundamental processes at work in generating spin supercurrents and controlling them, this work will pave the way for important new research directions exploiting this novel phenomenon.