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Inhomogeneous magnetism and superconductivity

非均匀磁性和超导性

基本信息

批准号：
EP/F016646/1
负责人：
James Annett
金额：
$ 13.89万
依托单位：
University of Bristol
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FF016646%2F1
关键词：
Inhomogeneous magnetism superconductivity

项目摘要

The past fifteen years has seen considerable research into the coupling of superconductivity and magnetism. These two effects are both mediated by coupling between electrons, but ferromagnetism leads to the parallel alignment of spins while conventional (so called spin-singlet) superconductivity requires anti-parallel spin alignment. As a result the coupling of superconductivity into ferromagnets is generally much weaker than the coupling into non-magnetic metals (the so-called proximity effect). However, at very short-range (a few nanometres) the coupling between superconductivity and ferromagnetism at the interface between the two materials results in complex behaviour which is distinct from that of either material. Most notably, the pairs of electrons which are responsible for superconductivity have a rapidly oscillating phase in the ferromagnet which can lead to negative rather than positive supercurrents appearing in devices in which a thin ferromagnetic barrier separates two superconductors. Devices based on this effect are currently being developed for quantum computation. More controversially, a few very recent experiments have detected a much longer-ranged proximity effect in which superconductivity can penetrate a ferromagnet over distances of hundreds on nanometres. This effect seems to be confirmation of theoretical predications that if the magnetism is inhomogeneous (i.e. all the spins do not point in a single direction) or the electrons are 100% spin polarised then a so-called spin-triplet state of superconductivity should appear. The aim of our proposed project is to investigate carefully the conditions required for the formation of this spin-triplet state and to understand how to control it so that potential applications can be developed. In particular we will look at classes of ferromagnet which have a spiral rather than linear magnetic order, we will also grow artificial magnetic structures in which such spirals can be changed by applying a magnetic field and we will explore how the presence of magnetic domain walls (which are regions in which the magnetism changes direction in a material) affects the superconducting properties.

在过去的十五年里，人们对超导性和磁性的耦合进行了大量的研究。这两种效应都是通过电子之间的耦合来介导的，但铁磁性导致自旋平行排列，而传统（所谓的自旋单态）超导性需要反平行自旋排列。因此，超导性与铁磁体的耦合通常比与非磁性金属的耦合弱得多（所谓的邻近效应）。然而，在非常短的范围（几纳米）下，两种材料之间的界面处的超导性和铁磁性之间的耦合会导致与任何一种材料都不同的复杂行为。最值得注意的是，负责超导性的电子对在铁磁体中具有快速振荡的相位，这可能导致在薄铁磁势垒分隔两个超导体的设备中出现负超电流，而不是正超电流。目前正在开发基于这种效应的设备用于量子计算。更具争议性的是，最近的一些实验发现了一种更远距离的邻近效应，其中超导性可以在数百纳米的距离上穿透铁磁体。这种效应似乎证实了理论预测，即如果磁性不均匀（即所有自旋不指向单一方向）或电子 100% 自旋极化，则应该出现所谓的超导自旋三重态。我们提出的项目的目的是仔细研究形成这种自旋三重态所需的条件，并了解如何控制它，以便开发潜在的应用。特别是，我们将研究具有螺旋磁序而不是线性磁序的铁磁体，我们还将生长人造磁结构，其中可以通过施加磁场来改变这种螺旋，并且我们将探索磁畴壁（材料中磁性改变方向的区域）的存在如何影响超导特性。