Superconductivity in the presence of strong correlations and spin-orbit interactions

存在强相关性和自旋轨道相互作用的超导性

• 批准号: RGPIN-2017-04873
• 负责人: Marsiglio, Frank
• 金额: $ 1.82万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=710785
• 关键词: Superconductivity; presence; strong; correlations; spin

Much of what we understand about simple metals and semiconductors is based on a single-particle picture. Once we determine what one electron does, then any macroscopic current or response is determined by this single-particle behaviour, with slight modifications to account for the statistics of the many electrons. In recent decades, however, researchers have discovered more and more materials that support conduction --- that is, they show metallic behaviour, and turn out to have extremely interesting properties. By way of example, a class of the high temperature cuprate materials, epitomized by La2CuO4, are not conducting, but have fascinating magnetic behaviour. When doped, they are conductors, albeit poor ones, but eventually, at sufficiently low temperatures, they superconduct. The "low temperatures" at which this is achieved turn out to be much higher than in any previously discovered superconductor. Superconductivity is an example of a highly correlated state that cannot be understood in terms of single particles. Moreover, in these materials, even the normal state cannot be understood in terms of single-particle behaviour. There are now many families of materials where this type of scenario is played out; there are sufficiently different properties from family to family that family-specific explanations have been offered for the "glue" that gives rise to the correlations in each family. In this proposal we want to explore possible more universal origins of some of the peculiar behaviour in these materials. Our focus will be spin-orbit coupling, which is normally thought of as a single particle property, one in which the intrinsic angular momentum of an electron (i.e. its "spin") affects the motion of the electron and vice-versa. The usual theory of superconductivity treats spin and orbital motion separately, although many modifications have been made in the last 15 years because certain superconductors that consist of structures that lack inversion symmetry make this separation impossible. All superconductors, however, have some degree of spin-orbit coupling, and in this proposal we will revisit the theoretical formulation of superconductivity with spin-orbit coupling, particularly near the surface of the material, which is precisely where many experiments probe for superconducting properties. At the same time we will explore the nature of the superconducting state that arises not because of some "glue", but because of a more generic mechanism driven by quantum matter's tendency to always expand, i.e. through kinetic energy lowering. A deeper understanding of the driving mechanism will aid material scientists in their quest to develop materials that superconduct at higher temperatures, and ultimately make superconducting applications cheaper and more accessible.

我们对简单金属和半导体的许多了解都是基于单粒子的图景。一旦我们确定了一个电子的作用，那么任何宏观电流或响应都是由这种单粒子行为决定的，只需稍作修改就可以解释许多电子的统计数据。然而，近几十年来，研究人员发现了越来越多的支持导电的材料-也就是说，它们表现出金属行为，并被证明具有极其有趣的特性。例如，以La2CuO4为代表的一类高温铜酸盐材料不导电，但具有迷人的磁性行为。当掺杂时，它们是导体，尽管它们很差，但最终，在足够低的温度下，它们会超导体。事实证明，实现这一点的“低温”比之前发现的任何超导体都要高得多。 超导性是一种不能用单个粒子来理解的高度关联状态的例子。此外，在这些材料中，即使是正常状态也不能用单粒子行为来理解。现在有许多材料家族都在上演这种类型的场景；每个家族都有足够不同的属性，以至于针对每个家族中产生相关性的“粘合剂”提供了特定于家族的解释。在这项提议中，我们想要探索这些材料中一些特殊行为的可能更普遍的起源。我们的焦点将是自旋-轨道耦合，这通常被认为是一种单粒子性质，在这种耦合中，电子的固有角动量(即电子的“自旋”)会影响电子的运动，反之亦然。通常的超导性理论将自旋和轨道运动分开处理，尽管在过去15年里做出了许多修改，因为某些超导体由缺乏反转对称性的结构组成，使得这种分离是不可能的。然而，所有的超导体都有一定程度的自旋-轨道耦合，在这个建议中，我们将重新审视具有自旋-轨道耦合的超导电性的理论公式，特别是在材料表面附近，这正是许多实验探索超导性质的地方。同时，我们将探索超导态的本质，这种超导态的产生不是因为某种“胶合”，而是因为一种更普遍的机制，即通过降低动能来驱动量子物质总是膨胀的趋势。对超导驱动机制的深入了解将有助于材料科学家探索开发在更高温度下超导的材料，并最终使超导应用变得更便宜和更容易获得。