Generation, Imaging and Control of Novel Coherent Electronic States in Artificial Ferromagnetic-Superconducting Hybrid Metamaterials and Devices

凝聚态物理学家一直在寻找有趣的物质新状态和具有独特可开发特性的新材料，这些特性反映了将它们结合在一起的电子的复杂量子力学相互作用。这些电子特性有时可以近似为在材料内移动的单个电子的总和，例如简单金属或半导体（如硅）中电子的导电性。然而，当对材料的精确描述需要考虑到大量电子的集体和相关运动时，这些性质总体上更有趣。这种集体物理导致了人们熟悉的铁等材料的铁磁性，以及不太熟悉的超导现象。在后一种情况下，电子能够在不产生热量的情况下流过超导材料的大部分，从而使极高的电流成为可能。例如，核磁共振全身扫描仪所需的大型超导磁体就可以应用这种技术。磁性和超导性通常是对立的现象，因为它们涉及电子自旋的不同排列。自旋是电子的一种量子特性，它会产生内在磁场——它可以被想象成附着在每个电子上的微小指南针。在铁磁性中，所有的自旋都指向同一个方向，但在传统的超导中，电子形成成对（库珀对），其中自旋指向相反的方向。因此，铁磁性通常会破坏这些库珀对，从而使它们的自旋平行排列，从而产生超导性。凝聚态物理学家经常寻找铁磁性和超导性共存的新材料，因为这可能表明存在某种奇异的新形式的超导性（或其他新颖的量子态）。一个例子是自旋-三重态超导，其中库珀对的自旋倾向于平行排列而不是反平行排列。一种尝试产生这种奇异物质状态的方法是通过在彼此的上面沉积非常薄的超导和铁磁薄膜（几纳米厚）来生长人工材料。通过这种方式，最终结构的性质可以被调整，有时会导致它表现出在自然存在的块状材料中从未发现的行为。这方面的一个例子是一种独特的自旋三重态（所谓的奇频）超导，最近在这种类型的薄膜结构中得到了证明。如果利用先进的电子束光刻技术在薄膜平面上制作这种薄膜材料，以产生纳米级的附加图案和结构，那么人造材料的生产可以更进一步。这种方法不仅可以发现有趣的新量子相，还可以在未来的技术中利用有用的特性，比如量子计算。在这个项目中，我们汇集了一个专家团队，他们拥有各种各样的技能，可以对上述纳米结构材料的类型进行生长、模式、测量和理论研究。我们的方法的一个特别新颖的方面是使用强大的成像技术，包括中子、μ子、x射线和定制的扫描磁传感器，以获得对系统中表现出奇频三重态超导性的基本物理以及详细的磁和物理结构与它们的奇异性质之间的关系的独特见解。虽然该项目的基本目标是追求新的科学知识，但我们将寻找可能在未来找到应用的有趣效果和特性。

Condensed matter physicists are constantly looking for interesting new states of matter and new materials with unique exploitable properties which reflect the complex quantum mechanical interactions of the electrons that bind them together. These electronic properties can sometimes be approximated to the sum of individual electrons moving within the material, such as the electrical conduction of electrons in simple metals or semiconductors like silicon. The properties are on the whole more interesting, however, when an accurate description of the material needs to account for the collective and correlated motion of large numbers of electrons. Such collective physics leads to the familiar ferromagnetic properties of materials like iron and, less familiarly, the phenomenon of superconductivity. In the latter electrons are able to flow through the bulk of a superconducting material without generating heat and extraordinarily high electrical currents become possible. This finds application, for example, in the large superconducting magnets required for MRI body scanners. Magnetism and superconductivity are often antagonistic phenomena, since they involve different arrangements of the spins of electrons. Spin is a quantum property of electrons that gives rise to intrinsic magnetic fields - it can be visualised as a tiny compass needle attached to each electron. In ferromagnetism all the spins point in the same direction, but in conventional superconductivity the electrons form pairs (Cooper pairs) in which the spins point in opposite directions. Ferromagnetism therefore normally destroys these Cooper pairs, and hence superconductivity, by causing their spins to align parallel.Condensed matter physicists often look for new materials where ferromagnetism and superconductivity coexist, since this can suggest the presence of some exotic new form of superconductivity (or other novel quantum state). One example is spin-triplet superconductivity, in which the spins of a Cooper pair prefer to be aligned parallel rather than antiparallel. One way to try and engender such exotic states of matter is to grow artificial materials by depositing very thin superconducting and ferromagnetic films (a few nm thick) on top of one another. In this way the properties of the final structure can be tuned, sometimes leading it to exhibit behaviours that have never been found in naturally occurring bulk materials. An example of this is a unique kind of spin-triplet (so called odd-frequency) superconductivity that has recently been demonstrated in this type of thin film structure. The production of artificial materials can be taken a step further if one also patterns such thin film materials in the plane of the film using advanced electron beam lithography technology, to produce additional patterns and structures on the nanoscale. Such an approach could lead not only to the discovery of interesting new quantum phases, but could also to useful properties that could be exploited in future technologies, such as quantum computing.In this project we bring together a team of experts with a diverse range of skills that can grow, pattern, measure and undertake theoretical studies on the type of nanostructured materials discussed above. One particularly novel aspect of our approach is the use of powerful imaging techniques involving neutron, muons, X-rays and bespoke scanning magnetic sensors to gain unique insights into both the basic physics at play in systems exhibiting odd-frequency triplet superconductivity as well as the relation between the detailed magnetic and physical structures and their exotic properties. Although the basic aim of this project is the pursuit of new scientific knowledge, we will be looking for interesting effects and properties that might find future applications.