Topological metals

量子材料是一种固体，在这种固体中，量子力学通常与原子和亚原子的尺度有关，直接体现在宏观尺度上的可观察性质。这种“宏观量子现象”不仅从根本上是有趣的，而且具有重要的实践意义。可以肯定的是，在未来的技术中，我们将以比现在更具创造性的方式使用量子力学，正在进行的量子材料基础研究目前正在为此奠定基础。当固体中的电子发生相干作用时，宏观量子现象就会出现。这种相干行为可能是电子-电子相互作用的结果，超导可能是由此产生的最广为人知的宏观量子效应。另一个更微妙、最近才被发现的量子相干来源是电子结构拓扑，它在物理学中日益增长的重要性得到了2016年诺贝尔物理学奖的认可。虽然最初认为非平凡的电子结构拓扑的概念和相关的可观察现象可能只存在于绝缘体中，但最近已经确定，金属也可以是“拓扑的”。因此，该领域的研究重点已经从拓扑绝缘体转移到拓扑金属和半金属。*本研究的目标是发展一套完整的拓扑金属理论。理解金属固体物理性质的标准范例是朗道费米液体理论。这需要修改以描述在拓扑金属中出现的新现象。目前正在出现的理解是，这些新现象可能被理解为量子反常。量子反常是起源于高能物理的一个概念，描述了量子效应对经典对称性的破坏。这个概念在粒子物理的标准模型中是至关重要的。令人惊讶的是，它现在已经找到了进入非相对论凝聚态物理学的途径：这只是凝聚态物质和粒子物理学之间显著融合的一个例子，这一融合正在开始实现。这项拟议的研究将寻求发展对拓扑金属中量子反常的可观察表现的完整理解，这代表了一类全新的宏观量子现象，并可能对未来的量子技术产生重大影响。

Quantum materials are solids in which quantum mechanics, normally associated with the atomic and subatomic scales, directly manifests in their macroscopic scale observable properties. Such "macroscopic quantum phenomena" are not just interesting fundamentally but are also of great practical importance. It is certain we will be using quantum mechanics in much more creative ways than we are now in future technologies, and the ongoing fundamental study of quantum materials is currently laying the foundation for this. *** Macroscopic quantum phenomena arise when electrons in solids act coherently. Such coherent behavior may result from electron-electron interactions, superconductivity being perhaps the most well-known macroscopic quantum effect that arises from this source. Another, more subtle, and uncovered only recently, source of quantum coherence, is the electronic structure topology, whose growing importance in physics was recognized by the 2016 Physics Nobel Prize. While it was initially thought that the notions of nontrivial electronic structure topology and the associated observable phenomena may only exist in insulators, it has very recently been established that metals may also be "topological". The focus of the field has thus shifted from Topological Insulators to Topological Metals and Semimetals.*** The goal of the proposed research is to develop a complete theory of Topological Metals. The standard paradigm for understanding the physical properties of a metallic solid is the Landau Fermi liquid theory. This needs to be modified to describe new phenomena that arise in Topological Metals. The understanding that is currently emerging is that these new phenomena may be understood as Quantum Anomalies. Quantum anomaly is a concept, which originated in high energy physics, and describes violation of a classical symmetry by quantum effects. This concept is of crucial importance within the Standard Model of particle physics. Amazingly, it has now found its way into non-relativistic condensed matter physics: just one example of a remarkable convergence between condensed matter and particle physics, which is starting to materialize. The proposed research will seek to develop a complete understanding of the observable manifestations of quantum anomalies in topological metals, which represent an entirely new class of macroscopic quantum phenomena, and which are likely to significantly impact future quantum technology.***