Topological mesoscopic superfluidity of 3He

通过相对弱的原子间相互作用和量子零点运动的结合，氦保持液态直至绝对零度。它为研究强相互作用玻色子（4He）和费米子（3He）系统提供了模型。这些材料在凝聚态物理核心概念的发展中发挥了关键作用：玻色-爱因斯坦凝聚；宏观量子物理；拓扑相变；金属中电子的朗道-费米液体理论；非传统的超导;拓扑量子物质。最丰富的系统是超流体3He（分别在1996年和2003年获得诺贝尔奖），Volovik将其概念范围描述为“以3He为中心的宇宙”，在概念上与物理学的大多数主要领域有关。凝聚态系统的特点是在每一个现代技术。这项技术的发展依赖于新材料的发现和创造，这些新材料具有新相和意想不到的特性，以及将这些材料结合在一起的混合设备，越来越多地在纳米尺度上。最近，仅从对称破缺的角度对新相的理解在某些情况下已被证明是不够的。这就是拓扑量子物质（2016年诺贝尔奖）的概念。两类重要的量子物质是关注的中心：拓扑绝缘体和拓扑超导体。通常的绝缘体是不导电的，因为在满能带和空能带之间有一个能隙。但在拓扑绝缘体中，能带结构的动量空间拓扑必然引起导电表面激励。另一方面，当金属冷却到超导状态时，就会出现一个间隙。拓扑超导体也支持表面/边缘激励，并且有大量的努力来确定材料是块拓扑超导体。本项目将利用已知可整体支持两种不同拓扑超流体相的超流体3He，建立拓扑介观超流体的新研究方向。在纳米尺度的约束下，这种材料提供了一种独特的拓扑超导模型。这些材料的对称性和拓扑结构之间微妙的相互作用是一个悬而未决的问题。我们的方法是将3He限制在精确的工程几何形状中，以创建混合纳米结构，从而实现前所未有的控制程度。以液体压力作为库柏对直径的调谐参数的约束和周期结构将诱发新的超流体相，其序参量对称性将由核磁共振推断。这些材料将成为混合介观超流体系统的基石。激励出现在拓扑超流体的表面/边缘/界面。在与惰性物质的界面中，我们可以原位调整表面散射，混合结构中的阶梯形约束将创建最高质量的流体内部界面。研究了时间反转不变超流体3He-B的表面和边缘自旋电流及其与受限Anderson-Higgs序参量集体模式的耦合，以及与Cooper对直径相似的纳米线。我们的目标是探测表面马约拉纳模态的非局部响应。手性超流体3He-A的边缘态将通过预测质量和热输运中的异常霍尔效应来研究。界面态将通过热输运来研究。该项目具有强大的国际合作维度，包括与康奈尔大学，NIST和PTB（柏林）的合作伙伴关系。与来自美国、欧洲和日本的理论家合作是设计和解释实验的核心。科学仪器行业内的伙伴关系将从该项目的核心技术发展中产生短期影响。

Helium remains liquid down to the absolute zero of temperature through a combination of relatively weak interatomic interactions and quantum zero point motion. It provides models for studying systems of strongly interacting bosons (4He) and fermions (3He). These materials have played a key role in the development of concepts central to condensed matter physics: Bose-Einstein condensation; macroscopic quantum physics; topological phase transitions; the Landau Fermi liquid theory of electrons in metals; unconventional superconductivity; topological quantum matter. The richest system is superfluid 3He (recognized in the 1996 and 2003 Nobel Prizes), the conceptual reach of which is described by Volovik in terms of a "3He-centric universe", conceptually linked to most major fields of physics.Condensed matter systems feature in every modern technology. The development of this technology has relied on the discovery and creation of new materials with new phases and often unanticipated properties, as well as hybrid devices which combine these materials, increasingly on the nanoscale. Recently the understanding of new phases solely in terms of symmetry breaking has been shown to be inadequate in some cases. This is the notion of topological quantum matter (2016 Nobel Prize). Two important classes of quantum matter are at the centre of attention: topological insulators and topological superconductors. Usual insulators do not conduct electricity, because of an energy gap between filled and empty energy bands. But in a topological insulator the momentum space topology of the band structure necessarily gives rise to conducting surface excitations. On the other hand, as a metal is cooled into its superconducting state, a gap emerges. Topological superconductors also support surface/edge excitations, and there are substantial efforts to identify materials that are bulk topological superconductors.This project will exploit superfluid 3He, known to support two distinct topological superfluid phases in bulk, establishing the new research direction of topological mesoscopic superfluidity. Under nanoscale confinement, this material provides a unique model for topological superconductivity. The subtle interplay between symmetry and topology in these materials is an open question. Our approach will be to confine 3He in precisely engineered geometries to create hybrid nanostructures, allowing a degree of control that is unprecedented. Confinement and periodic structures, with liquid pressure as a tuning parameter of Cooper pair diameter, will induce new superfluid phases, for which the order parameter symmetry will be inferred from nuclear magnetic resonance. These materials will be building blocks for hybrid mesoscopic superfluid systems. Excitations emerge at surfaces/edges/interfaces of the topological superfluid. As well as the interface with inert matter, where we can tune surface scattering in situ, stepped confinement in hybrid structures will create intra-fluid interfaces of the highest quality. Surface and edge spin currents in time reversal invariant superfluid 3He-B will be investigated by NMR and their coupling to confined Anderson-Higgs order parameter collective modes, as well as nano-wires of diameter similar to that of Cooper pairs. Our ambition is to detect non-local response of the surface Majorana modes. Edge states in chiral superfluid 3He-A will be investigated by a predicted anomalous Hall effect in mass and thermal transport. Interface states will be investigated by thermal transport. This project has a strong international collaborative dimension, including partnerships with Cornell, NIST and PTB (Berlin). Partnerships with theorists from the USA, Europe and Japan are central to the design and interpretation of experiments. Partnerships within the scientific instruments industry will deliver short-medium term impact from the technical developments central to this project.