Discovering twisted bilayer materials with strong electron correlations

发现具有强电子相关性的扭曲双层材料

基本信息

批准号：
EP/S025324/1
负责人：
Johannes Lischner
金额：
$ 56.72万
依托单位：
Imperial College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2019
资助国家：
英国
起止时间：
2019 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FS025324%2F1
关键词：
Discovering twisted bilayer materials strong

项目摘要

Materials with strong electron correlations exhibit fascinating properties with potential applications in energy and information technology but understanding and quantitatively predicting their behaviour remains one of the grand challenges of condensed matter and materials physics. Taking the high-transition-temperature (high-Tc) superconducting cuprates as an example, despite several decades of study there is still no clear consensus on the mechanism of superconductivity and even the normal state from which the superconducting state arises is not fully understood. The recent discovery of insulating behaviour and unconventional superconductivity in twisted bilayer graphene (TBG) has generated tremendous excitement and established twisted bilayers of 2d materials as a new platform for studying the "strong-correlation puzzle". In particular, these systems allow for an unprecedented level of control (eg, compared to oxide materials such as the cuprates) as the strength of electron correlations is tunable via the twist angle and the electron density can be modified through application of an electric field. Besides TBG, there exists a large and almost entirely unexplored chemical space of potentially interesting strongly correlated twisted bilayer materials that result from combinations of the approximately 1,825 2d materials that are potentially exfoliable. The field of strongly-correlated twisted bilayer materials is nascent. Many different mechanisms have been proposed to explain the experimentally-observed insulating behaviour in TBG, without any clear consensus. Similarly, there is no agreement regarding the origin and properties of the superconducting state. The discrepancies among these theoretical predictions arise from the use of simplified Hamiltonians and/or approximations in the description of electron-electron interactions. There is, therefore, a clear and present opportunity to develop a microscopic, parameter-free and first-principles-based understanding of strong correlations in existing twisted bilayer materials and to explore the chemical space of 2d materials for new twisted bilayer systems with strong and tunable electron correlations.In this proposal we will develop a new method that combines first-principles density-functional theory calculations with state-of-the-art functional renormalisation group methods to calculate, with no adjustable parameters, phase diagrams of twisted bilayer materials as a function of doping, temperature and twist angle. First, we will apply our method to TBG and twisted graphene on boron nitride (TGBN) with the aim of resolving the current controversies regarding the origin of the insulating behaviour and superconductivity in these systems. Then we will use it to create a high-throughput computational workflow to discover new bilayer materials with strong electron correlations that give rise to unconventional phases, including superconductivity, charge and spin density waves, spin liquids or Mott insulators. This will enable us to guide experimental efforts in the direction of the most promising candidate systems and could potentially result in novel devices for energy and information technology that combine the advantages of 2d materials with the tunabiliy of strongly correlated systems.

具有较强电子相关性的材料在能源和信息技术中具有潜在的应用表现出引人入胜的特性，但是理解和定量预测其行为仍然是凝结物质和材料物理学的巨大挑战之一。以高过渡 - 温度（高-TC）超导粉提曲为例，尽管研究了几十年，但仍未完全了解超导性的机制，甚至超导状态的正常状态仍未得到完全了解。扭曲的双层石墨烯（TBG）中最近发现绝缘行为和非常规超导性的发现，引起了极大的兴奋，并确立了2D材料的扭曲双层，作为研究“强相关拼图”的新平台。特别是，这些系统允许使用前所未有的控制水平（例如，与氧化物材料（例如铜）相比），因为电子相关性的强度是通过扭角来调谐的，并且可以通过应用电场来修改电子密度。除TBG外，还有一个可能有趣的扭曲的双层材料的大型且几乎完全未开发的化学空间，这是由于大约1,825 2D材料的组合而产生的，这些材料可能会被剥落。强相关的扭曲双层材料的领域是新生的。已经提出了许多不同的机制来解释TBG中实验观察到的绝缘行为，而没有任何明确的共识。同样，关于超导状态的起源和特性也没有达成共识。这些理论预测之间的差异是由于使用简化的哈密顿人和/或近似电子相互作用的近似值引起的。因此，有一个明确而目前的机会来开发微观，无参数和第一原理对现有扭曲双层材料中强相关性的理解，并探索具有强大和强的扭曲双层系统的2D材料的化学空间在此提案中，我们将开发一种新方法，将第一原理密度功能理论计算与最新的功能性ren级化方法进行计算，以计算，没有可调节的参数，扭曲的双层材料的相图作为相图掺杂，温度和扭角的功能。首先，我们将我们的方法应用于硝酸硼（TGBN）上的TBG和扭曲石墨烯，目的是解决有关这些系统中绝缘行为和超导性的目前争议。然后，我们将使用它来创建一个高通量计算工作流程，以发现具有较强电子相关性的新的双层材料，这些材料会引起非常规阶段，包括超导性，电荷和自旋密度波，旋转液体或mott绝缘子。这将使我们能够指导最有前途的候选系统的方向实验性工作，并有可能为能源和信息技术提供新颖的设备，这些设备将2D材料的优势与密切相关的系统的图比相结合。