Exploring connections between superconductivity, unconventional quantum order, and Fermi surface reconstruction

我们正处于一场材料革命之中，这场革命正在改变计算、太阳能、强材料等技术的面貌。 超导性在未来的发电和传输、量子计算、运输和磁体技术中发挥着重要作用。然而，这个未来取决于我们探索新材料系统的能力，以及更好地理解非常规超导性的能力。 超导体物理学的巨大进步源于重费米子，高Tc氧化铜和铁磷族元素化物超导体的发现，但这些发现揭示了我们不理解的深层物理问题，关于超导性，低温磁相变，特别是费米表面重建的令人惊讶的交织物理。对这些问题的探索产生了新的和意想不到的物理学。我自己的研究小组，在我们最近的研究在这一领域，已导致了广泛的主题：拓扑半金属状态的烧绿石铱酸盐，“非金属金属”的行为受挫的磁性金属，奇异的量子磁性与费米表面跃迁，并结合核电子序参数与一种新的量子临界点在镨基超导体。 与此同时，我们增加了新的实验能力，因此我们现在拥有的压力单元可以达到400毫巴，温度低至10 mK，磁场高达18特斯拉。我们用这些在复杂物质中创造新的状态。 现在，我们希望增加新的功能：在高压体积内施加非常大的单轴应力的能力;使用电子结构计算来指导我们的压力或单轴应力测量;以及使用现代聚焦离子束样品制备来快速可靠地制备高压测量。 这些发展为研究生提供了一个很好的训练基地，也将使我们能够迅速发展。 在此期间，我们将把我们的能力应用于各种有前途的材料，因为我们也将继续努力了解我们小组的最新发现。前者的一个例子是Sr 2 RhO 4，它是高温和拓扑超导体的表亲。它有一个扭曲的钙钛矿结构，我们将使用电子结构计算来了解如何最好地施加压力来驱动一个非常平坦的能带，靠近费米能，穿过费米能，引起一个主要的费米表面重建，我预测，超导性，甚至高温超导性。 正在进行的项目的一个例子是与英国的一个小组进行的一项新的合作，以探索低于1毫开尔文的核电子组合秩序。 我们的最终目标是新的和改进的超导技术，但沿着有很多新的物理探索。

We are in the midst of a materials revolution that is changing the face of technologies such as computation, solar energy, strong materials, and beyond. Superconductivity has an important future role to play, in power generation and transmission, quantum computing, transportation, and magnet technology. This future, however, depends on our ability to explore new materials systems, and to better understand unconventional superconductivity. A huge advance in the physics of superconductors resulted from the discovery of heavy fermion, high-Tc copper-oxide, and iron-pnictide superconductors, but these discoveries revealed that there are deep physics issues that we don't understand, regarding the surprisingly intertwined physics of superconductivity, low-temperature magnetic phase transitions and, especially, Fermi surface reconstruction. The exploration of these issues has produced new and unexpected physics. My own research group, in our recent studies in this field, has been led into a broad range of topics: topological semi-metallic states in pyrochlore iridates, 'non-metallic metal' behaviour in frustrated magnetic metals, exotic quantum magnetism associated with Fermi surface transitions, and combined nuclear-electronic order parameters with a new kind of quantum critical point in praseodymium-based superconductors. At the same time we have added new experimental capabilities, so that we now have pressure cells that can reach 400 kilobar, and temperatures down to 10 mK, in magnetic fields up to 18 tesla. We use these to create novel states in complex matter. Now we want to add new capabilities: the ability to apply very large uniaxial stress within a high-pressure volume; to use electronic structure calculations to guide our pressure or uniaxial stress measurements; and to use modern focussed-ion-beam sample preparation to rapidly and reliably prepare high-pressure measurements. Such developments offer an excellent training ground for research students, and they will also allow us to advance rapidly. During this grant we will apply our capabilities to a variety of promising materials, as we also continue to work to understand recent discoveries in our group. An example of the former is Sr2RhO4, which is a cousin to high-temperature and topological superconductors. It has a distorted perovskite structure, and we will use electronic-structure calculations to understand how best to apply pressure to drive a very flat band, near the Fermi energy, across the Fermi energy, causing a major Fermi surface reconstruction and, I predict, superconductivity, perhaps even high temperature superconductivity. An example of an ongoing project is a new collaboration with a group in the UK to explore combined nuclear-electronic order to below 1 millikelvin. Our ultimate goal is new and improved superconducting technologies, but along the way there is a lot of new physics to explore.