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Harnessing disorder to tune, tailor and design classical and quantum spin liquids

利用无序来调整、定制和设计经典和量子自旋液体

基本信息

批准号：
EP/T028041/1
负责人：
J P Goff
金额：
$ 36.32万
依托单位：
Royal Holloway University of London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2021
资助国家：
英国
起止时间：
2021 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FT028041%2F1
关键词：
Harnessing disorder tune tailor design

项目摘要

Entanglement underpins many of the defining non-classical properties of quantum mechanics, and long-range entanglement engenders exotic phenomena such as fractional quantum numbers and emergent topological excitations. The next generation quantum technologies will rely on our understanding and exploitation of coherence and entanglement, and this proposal directly tackles these issues. Exemplars of massive long-range entangled phases are quantum spin liquids -- states of quantum magnets in which electronic spins reside in macroscopic superpositions of infinitely many disordered, liquid-like microstates. Frustrated pyrochlore magnets often exhibit liquid-like short-range correlations down to the lowest temperatures and are therefore ideal candidate materials to look for classical and quantum spin liquid behaviour. The presence of disorder in any of its forms -- fluctuations, strain, structural defects -- is usually regarded as a nuisance that has the potential to obscure or disrupt the sought-after spin liquid phase. However, it has also been recently shown that the presence of structural disorder can sometimes stabilise classical and quantum spin liquids, and it can even lead to new magnetic degrees of freedom, the formation of topological spin glasses and the formation of entirely novel quantum spin liquids. Inspired by these results, we here take the view of disorder as a resource to tailor, tune and control spin liquid behaviour and quantum entanglement. Specifically, we propose to introduce structural disorder in pyrochlore materials in a controlled manner via doping, and to determine the defect structures using single-crystal diffuse neutron scattering. The results from these measurements will allow us to develop theoretical models and simulations to understand how the defects change the magnetic properties of the ions and their collective behaviour. In parallel to candidate materials for quantum spin liquid behaviour, we will also study related materials in the so-called `classical' regime, where the properties without disorder are better understood and where modelling and simulation capabilities are generally greater; in doing this we shall provide insight and support to the analysis of the more challenging quantum regime. In our concerted theory-experiment approach, we expect the insight from modelling to feed back into deciding which further samples to grow and which measurements to perform to test our predictions, ranging from thermodynamic measurements to dynamical structure factors using polarized neutrons. We will investigate questions about the stability of quantum spin liquid phases; the promotion of quantum fluctuation due to effective transverse fields introduced by disorder; the scattering and trapping of emergent excitations, and in general questions about localisation and glassiness, in response to the disorder produced by structural distortions. Our overarching aim is to investigate the relationship between topology, glassiness and liquidity, and to obtain unambiguous evidence for long-range entanglement in quantum spin liquids.

纠缠是量子力学许多定义的非经典性质的基础，长程纠缠会产生奇异的现象，例如分数量子数和涌现的拓扑激发。下一代量子技术将依赖于我们对相干性和纠缠的理解和利用，而该提案直接解决了这些问题。大规模长程纠缠相的例子是量子自旋液体——量子磁体的状态，其中电子自旋处于无限多个无序、类液体微观状态的宏观叠加中。受阻烧绿石磁体通常在最低温度下表现出类似液体的短程相关性，因此是寻找经典和量子自旋液体行为的理想候选材料。任何形式的无序的存在——波动、应变、结构缺陷——通常被认为是一种麻烦，有可能掩盖或破坏备受追捧的自旋液相。然而，最近也表明，结构无序的存在有时可以稳定经典和量子自旋液体，甚至可以导致新的磁自由度、拓扑自旋玻璃的形成以及全新的量子自旋液体的形成。受这些结果的启发，我们将无序视为定制、调整和控制自旋液体行为和量子纠缠的资源。具体来说，我们建议通过掺杂以受控方式在烧绿石材料中引入结构无序，并使用单晶扩散中子散射来确定缺陷结构。这些测量的结果将使我们能够开发理论模型和模拟，以了解缺陷如何改变离子的磁性及其集体行为。除了量子自旋液体行为的候选材料之外，我们还将研究所谓“经典”体系中的相关材料，在这种体系中，无序特性可以得到更好的理解，建模和模拟能力通常也更强；在此过程中，我们将为更具挑战性的量子体系的分析提供见解和支持。在我们协调一致的理论实验方法中，我们期望从建模中获得的见解能够反馈到决定进一步生长哪些样本以及执行哪些测量来测试我们的预测，范围从热力学测量到使用极化中子的动态结构因子。我们将研究有关量子自旋液相稳定性的问题；由于无序引入的有效横向场而促进量子涨落；新兴激发的散射和捕获，以及关于局部化和玻璃性的一般问题，以响应结构扭曲产生的无序。我们的首要目标是研究拓扑、玻璃性和流动性之间的关系，并获得量子自旋液体中长程纠缠的明确证据。