Topological mesoscopic superfluidity of 3He

氦通过相对较弱的原子间相互作用和量子零点运动的组合，保持液态，直到温度的绝对零度。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；非传统超导；拓扑量子物质。最丰富的系统是超流体3He(在1996年和2003年的诺贝尔奖中被认可)，沃洛维克将其概念范围描述为“以3He为中心的宇宙”，在概念上与大多数主要物理领域有关。凝聚态物质系统出现在每一种现代技术中。这项技术的发展依赖于具有新相和往往意想不到的性能的新材料的发现和创造，以及越来越多地在纳米尺度上结合这些材料的混合设备。最近，仅从对称性破缺的角度来理解新相在某些情况下已被证明是不充分的。这就是拓扑量子物质的概念(2016年诺贝尔奖)。人们关注的焦点是两类重要的量子物质：拓扑绝缘体和拓扑超导体。通常的绝缘体不导电，因为充满和空载能带之间存在能隙。但在拓扑绝缘体中，能带结构的动量空间拓扑必然会引起表面激励。另一方面，当金属冷却到超导状态时，就会出现缺口。拓扑超导体也支持表面/边激发，在识别体拓扑超导体材料方面有很大的努力。本项目将利用超流3He，它支持两个不同的体相拓扑超流，建立拓扑介观超流的新的研究方向。在纳米尺度的约束下，这种材料为拓扑超导提供了一个独特的模型。这些材料中对称性和拓扑学之间微妙的相互作用是一个悬而未决的问题。我们的方法将是将3He限制在精确设计的几何形状中，以创建混合纳米结构，从而实现前所未有的程度控制。以液体压力为库珀对直径的调谐参数的禁闭和周期结构将产生新的超流相，其有序参数的对称性将由核磁共振推断出来。这些材料将成为混合介观超流体系统的基石。在拓扑超流体的表面/边缘/界面处出现激发。除了与惰性物质的界面，我们可以就地调整表面散射，混合结构中的阶梯限制将创建最高质量的流体内界面。用核磁共振方法研究了时间反转不变超流体3He-B中的表面和边缘自旋流及其与受限的Anderson-Higgs序参数集合模的耦合，以及直径类似于Cooper对的纳米线。我们的目标是探测地表Majorana模的非局域响应。手性超流3He-A中的边态将通过预言的质量和热输运中的反常霍尔效应来研究。界面态将通过热输运进行研究。该项目具有很强的国际协作性，包括与康奈尔大学、NIST和PTB(柏林)的伙伴关系。与美国、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这一项目的核心技术发展中产生短期和中期影响。

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.