Designing and exploring new quantum materials based on Fermi surface topological transitions

电子技术在过去几十年中取得的进步是通过完善对材料中非相互作用电子的控制而实现的。现在可以可靠地获得这种控制，例如，在简单的金属和半导体中，通过调整费米能和有效电子质量。然而，由于这种材料所表现出的电子性质的范围从根本上受到限制，这种技术已经达到了其潜力的极限。如果在电子之间的强相互作用引起有趣的宏观量子现象的系统中建立对集体电子行为的可靠控制，就可以实现戏剧性的突破。多铁性、自旋电子材料中的巨磁电阻、聚合物系统中的电子相关性和高温超导性只是具有巨大应用潜力的几个例子。量子计算机，预计将彻底改变现代世界，并在原则上设想良好，仍然无法实现，由于缺乏可靠的控制材料基础。这在很大程度上是因为电子关联物理学的先验精确理论基础，这将允许随意设计所需的电子特性，仍然是一个挑战，目前还没有。为了描述固体中相互作用的电子效应，费米液体（FL）理论一直是一个强有力的起点。其应用的显著成就包括常规超导的微观理论和液态氦-3的物理学。即使在FL理论被证明不充分的情况下，它的失败也为新的发现铺平了道路，并且在许多情况下，结果决定了新的方向。一个中心概念，自然出现在FL的背景下，但相关的远远超出了基本FL理论所描述的情况下，是费米面（FS）和态密度（DOS）的概念在不同的部分FS。在高DOS的地方，相互作用效应可能变得更加明显，系统的性质可以通过它们来控制。高DOS值甚至奇异值的DOS伴随着不同类型的FS的拓扑变化。在这个项目中，我们将建立在种子工作，我们将继续分类，使用先进的数学工具，在DOS中的奇点，并建立一个全面的了解相互作用的影响。这项理论工作将伴随着广泛的搜索，通过第一原理计算，新的量子材料，可以作为不同类别的奇点的例子。我们的实验合作伙伴热衷于制造和制造将被识别的新材料。与此同时，现有的材料，如锶铼酸盐和二维金属硫属化物，具有无法解释和未探索的性质，具有巨大的科学兴趣和潜在的技术应用，将提供直接的操场来测试我们的理论的力量。虽然这些想法非常集中，但拟议工作的范围和影响非常广泛，因此凝聚态理论和实验领域的几位世界领导人的共同努力是实现所有目标所必需的。因此，这一合作项目涉及来自三个不同国家的八个机构的研究人员、学术访问者和项目伙伴。

The advances in electronic technology that have been achieved over the last few decades have been enabled by perfecting control over non-interacting electrons in materials. This control can now be reliably obtained, e.g., in simple metals and semiconductors, by tuning the Fermi energy and the effective electron mass. However, this technology has reached the limit of its potential due to the fundamentally limited range of electronic properties exhibited by such materials. A dramatic breakthrough can be achieved if one establishes reliable control over collective electronic behaviour in systems where strong interactions between electrons give rise to intriguing macroscopic quantum phenomena. Multiferroics, giant magnetoresistance in spintronic materials, electron correlations in polymeric systems, and high-temperature superconductivity are just are a few examples with vast potential for novel applications. A quantum computer, expected to revolutionise the modern world, and well-envisaged in principle, can still not be realised due to the lack of reliably controlled material base. The reason, largely, is that a priori accurate theoretical underpinning of electron correlation physics, which would allow to design desired electronic properties at will, has remained a challenge and is currently missing.To describe effects of interacting electrons in solids, Fermi liquid (FL) theory has been a powerful starting point. Notable successes of its application include the microscopic theory of conventional superconductivity and the physics of liquid Helium-3. Even in cases where FL theory has proven inadequate, its failure paved the way for new discoveries, and in many cases the results dictated the new directions. A central concept, naturally emerging in the FL context but relevant far beyond the cases described by the basic FL theory, is the notion of the Fermi Surface (FS) and the density of states (DOS) at different parts of the FS. In places with high DOS the interaction effects may become more pronounced and the properties of the system can be governed through them.High, or even singular values of DOS are accompanied by topological changes of the FSs of different types. In this project, we will build on seed work and we will continue the classification, using advanced mathematical tools, of the singularities in DOS and to build a comprehensive understanding of the effects of interactions. This theoretical work will be accompanied by a wide search, through first principles calculations, of new quantum materials that can serve as examples of the different classes of singularities. Our experimental partners are keen to fabricate and characterise the new materials that will be identified. In parallel, existing materials, such as strontium ruthenates and the two-dimensional metallic chalcogenides with unexplained and unexplored properties which are of enormous scientific interest with potential technological applications, will provide the immediate playground to test the power of our theories. Although the ideas are very focused, the scope and the impact of the proposed work is very wide, therefore a concerted effort of several world leaders in condensed matter theory and experiments is necessary to achieve all the objectives. As a result, this collaborative project involves researchers, academic visitors and project partners from eight institutions in three different countries.