Correlated Phases in Novel Superconductors and Ultracold Atomic Gases

将电子视为不相互作用的波状电子，对金属和半导体等材料进行了令人惊讶的成功的量子描述，这些材料构成了我们今天认为理所当然的电子产品的基础。当人们考虑到负电荷电子之间库仑相互作用的大小时，这幅图的成功就更加引人注目--人们只需经历静电，就可以欣赏到微小的电荷不平衡可以产生的可测量的影响。因此，物理学家们越来越多地发现强关联系统，在这些系统中，简单的、非相互作用的理论不再有效，这或许就不足为奇了。一个最好的例子是超导体，在超导体中，电子在低温下形成对，然后在没有任何阻力的情况下流动。的确，从原理上讲，超导体中的电流可以永远流动。虽然这种配对现象在许多超导材料中都得到了很好的理解，但近几十年来出现了新的超导体类别，它们通常与磁性有关，而且超导体的温度比传统理论预测的要高得多。显然，对这些强关联材料的正确理解不仅仅是一种深奥的追求：室温下无损耗电流的可能性将对能源效率产生重大影响。理论家面临的巨大挑战是开发新的概念，超越目前相互作用较弱的描述。朝这个方向迈出的一小步是，首先解决强关联现象的简单版本。幸运的是，物理学家现在拥有操纵和控制被光和磁场捕获的原子的冷气体的技术能力，因此这些系统提供了研究简单模型的理想环境。我已经积极参与了强相互作用原子超流体理论的开发，这种理论可以被视为超导体的中性类似物。这些系统的最终优势是能够一次解决每个变量，例如相互作用强度，从而分离出强关联现象背后的基本物理。理想情况下，人们需要一个跨学科的理论研究计划，将非传统超导体与原子气体模型并行考虑，这就是拟议研究的性质。除了探索冷原子气体中的超流性和磁性的模型系统外，我的目标是研究铁基超导体，这是一种新发现的高温超导体，有望为其他新型超导体提供启示。其关键思想是，对简单工程原子系统的研究可以让我深入了解铁基超导体，而非传统超导体的谜题可以指导我对原子气体中相关现象的研究。这一点，再加上每个高度活跃领域的实验的投入，有望使我们更接近于更完整地理解相互作用的系统。

The treatment of electrons as non-interacting and wave-like has yielded an amazingly successful quantum description of materials like metals and semiconductors, which form the basis of the electronics that we take for granted today. The success of this picture is all the more remarkable when one considers the size of the Coulomb interaction between the negatively-charged electrons - one only has to experience static electricity in order to appreciate the measurable effects that a small imbalance of charge can have. Thus, it is perhaps no surprise that physicists are increasingly discovering strongly-correlated systems where simple, non-interacting theories are no longer valid. A prime example is the superconductor, in which electrons form pairs at low temperatures and then flow without any resistance. Indeed, an electrical current in a superconductor can, in principle, flow forever. While this pairing phenomenon is well understood in many superconducting materials, new classes of superconductors have emerged in recent decades that are generally associated with magnetism and which superconduct at much higher temperatures than predicted by conventional theory. Clearly, developing a proper understanding of these strongly-correlated materials is more than just an esoteric pursuit: the possibility of lossless electrical current at room temperature would have a major impact on energy efficiency. The formidable challenge for the theorist is to develop fresh concepts that go beyond the current weakly-interacting descriptions. One small step in this direction is to first tackle simple versions of strongly-correlated phenomena. Fortunately, physicists now have the technological capacity to manipulate and control cold gases of atoms that have been trapped by light and magnetic fields, and thus these systems provide the ideal environment in which to study simple models. Already, I have been heavily involved in developing theories of strongly-interacting atomic superfluids , which can be regarded as neutral analogues of superconductors. The ultimate advantage of these systems is the ability to address each variable, e.g. interaction strength, one at a time and thus isolate the basic physics underlying strongly-correlated phenomena. Ideally one needs a programme of interdisciplinary theoretical research that considers unconventional superconductors in parallel with models of atomic gases, and this is the nature of the proposed research. As well as exploring model systems of superfluidity and magnetism in cold atomic gases, I aim to investigate the iron-based superconductor, a newly-discovered class of high-temperature superconductor that promises to shed light on other novel superconductors. The key idea is that the study of simple engineered atomic systems can lend insight into the iron-based superconductors, while the puzzles of unconventional superconductors can direct my research on correlated phenomena in atomic gases. This, together with input from the experiments in each highly active field, would hopefully bring us closer to a more complete understanding of interacting systems.