Disorder induced superconductivity in quasi 1-D strongly correlated systems

准一维强相关系统中的无序诱导超导性

• 批准号: 2003683
• 金额: --
• 依托单位: Aston University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2003683
• 关键词: Disorder; induced; superconductivity; quasi; strongly

AbstractThe long-lasting search for superconducting materials where the phase transition temperature can be increased by the introduction of disorder has been unsuccessful until recently. Only recently, advances in controlled incorporation of disorder in quasi-one-dimensional materials proved the existence of such materials. The discovery of new materials where superconducting pairing is enhanced by disorder opens a path to controlling (increasing) the transition temperature. Such systems are not described by standard mean-field theories of phase transitions. We will develop a new quantum field theory for quasi-one-dimensional strongly correlated disordered superconductors required to understand the nature of the new superconducting state.ContextAttraction between electrons leads to the formation of a superconductor. Disorder localises electrons and, therefore, suppresses their transport, leading to the formation of an 'antipode' state with infinite resistance, insulator. The competition between these two mechanisms is usually formulated as disorder-induced suppression of superconductivity. This fact has been known for decades and the main open question which was "how exactly the temperature of the transition into a superconducting state is suppressed by the disorder". Unexpectedly, recent experiments on different materials demonstrated an increase in the transition temperature, so-called 'critical temperature enhancement'. These materials turned out to be one-dimensional chains with extremely weak couplings between them. In one dimension there can be no true superconductivity and any disorder localises electrons. Nevertheless, it seems that a weak coupling between one-dimensional chains creates a new state with superconducting behaviour which is enhanced by the disorder. There is no theory at the moment capable of explaining the observed behaviour. This project is focused on developing such a theory; the aim is to understand the nature of disorder-induced enhancement of phase transition temperature, open the path to controlling the superconducting properties, and to guide the search for novel high-temperature superconductors.ObjectivesTo understand the nature of disorder-induced emergence and enhancement of superconductivity, we will implement an exhaustive theoretical study of phase transitions taking place in novel quasi-one-dimensional materials. The research objectives are: 1. Formulation of the effective field theory describing disordered system of coupled one-dimensional electron liquids with superconducting pairing. 2. Theoretical analysis of the multi-fractal nature of many-electron wavefunctions in quasi-one-dimensional systems of coupled electron liquids. 3. Theoretical test of the hypothesis that enhancement of phase transition temperature is related to the topology of the wavefunctions support in different network-like structures and materials. MethodA description of phase transitions in low-dimensional systems (where almost all interactions lead to non-perturbative effects) requires application of quantum field theory in a form suitable to dealing with condensed matter problems. A one-dimensional electron liquid is treated by the bosonisation technique. To describe a set of coupled one-dimensional electron liquids we will have to build corresponding field-theoretic model that generalizes bosonisation approach and includes disorder and superconductivity. The presence of disorder will require statistical averaging that will be performed with the use of the Keldysh-based or replica approach. To analyse different mechanisms leading to formation of a new state, we will use renormalisation group analysis. For the analysis of superconductivity onset in lattices with non-trivial topology (Bethe lattice and scale-free networks) we will use a combination of non-linear sigma model and the cavity method.

通过引入无序来提高相变温度的超导材料的长期研究直到最近才取得成功。直到最近，在准一维材料中控制无序结合的进展证明了这种材料的存在。新材料的发现，其中超导配对被无序增强，开辟了一条控制（增加）转变温度的道路。这样的系统不能用相变的标准平均场理论来描述。我们将发展一种新的量子场论，用于准一维强关联无序超导体，以理解新超导态的性质。无序使电子局域化，从而抑制它们的传输，导致形成具有无限电阻的“对极”状态，绝缘体。这两种机制之间的竞争通常被表述为无序诱导的超导抑制。这一事实几十年来一直为人所知，主要的未决问题是“如何准确地过渡到超导状态的温度被无序抑制”。出乎意料的是，最近对不同材料的实验表明，转变温度的增加，所谓的“临界温度提高”。这些材料原来是一维链，它们之间的耦合非常弱。在一维空间中，不可能有真正的超导性，任何无序都会使电子局域化。尽管如此，一维链之间的弱耦合似乎创造了一个具有超导行为的新状态，这种超导行为被无序增强。目前还没有理论能够解释观察到的行为。本项目的重点是发展这样一种理论;目的是了解无序诱导相变温度增强的本质，打开控制超导性质的途径，并指导寻找新的高温超导体。目的为了了解无序诱导超导电性的出现和增强的本质，我们将对发生在新型准一维材料中的相变进行详尽的理论研究。本研究的目的是：1.描述具有超导配对的一维耦合电子液体无序系统的有效场论公式。2.准一维耦合电子液体系统中多电子波函数多重分形性质的理论分析。3.对相变温度的提高与不同网络结构和材料中波函数拓扑结构有关的假设进行了理论检验。低维系统（几乎所有的相互作用导致非微扰效应）中的相变的描述需要以适合于处理凝聚态问题的形式应用量子场论。用玻色化技术处理一维电子液体。为了描述一组耦合的一维电子液体，我们必须建立相应的场论模型，推广玻色化方法，并包括无序和超导性。无序的存在将需要统计平均，将使用基于Keldysh或复制的方法进行。为了分析导致新状态形成的不同机制，我们将使用重整化群分析。对于具有非平凡拓扑结构的晶格（Bethe晶格和无标度网络）中的超导起始点的分析，我们将使用非线性sigma模型和腔方法的组合。