Nonequilibrium and dissipative effects in topological materials

20世纪初量子物理学的发展彻底改变了人们对材料的认识。根据量子物理定律，固体被分为绝缘体、半导体、金属和超导体。几十年来，人们一直认为，所有的绝缘体在不能导电时都是相似的，而当涉及到它们极端的载流能力时，所有超导体也都是相似的。 这种信念最初在1980年被动摇，然后在六年前被打破，当时很明显，电子在固体中的行为也可以用一个被称为拓扑学的数学分支来分类。例如，根据固体的拓扑学分类，一些绝缘体(称为“拓扑型”绝缘子)在其表面导电，而另一些绝缘体(称为“非拓扑型”或“普通”绝缘体)则不导电。拓扑绝缘体表面的金属是非常特殊的：电子是失重的，它们的导电性非常强，它们的磁性也很特殊。 尽管拓扑材料的出现及其技术前景点燃了研究活动的火花，但到目前为止，大多数研究都集中在平衡(与时间无关)的设置上，以及电子与环境隔离的情况下。不幸的是，平衡假设排除了一些有趣的技术应用，孤立电子的假设通常是不现实的。因此，为了开发有益于社会的有用的拓扑器件，研究拓扑材料中的电子是如何受到外部扰动及其非电子环境的影响是至关重要的。这项调查确实是我研究计划的主要目标。

The development of quantum physics in the beginning of the 20th century revolutionized people's understanding of materials. Based on the laws of quantum physics, solids were classified into insulators, semiconductors, metals, and superconductors. For decades, it was believed that all insulators were similar to one another when it came to their inability to conduct electricity, and that all superconductors were also similar to one another when it came to their extreme ability to carry electrical current. Such belief was first shaken in 1980, and then shattered six years ago, when it became apparent that the behavior of electrons in solids can also be classified using a branch of mathematics known as topology. For example, according to the topological classification of solids, some insulators (dubbed "topological" insulators) conduct electricity on their surfaces whereas others (dubbed "non-topological" or "ordinary" insulators) do not. The metal at the surface of a topological insulator is quite special: electrons are weightless, their conduction of electricity is remarkably robust, and their magnetic properties peculiar. Although the advent of topological materials and their technological promise have ignited a spark of research activity, most of the studies thus far have focused on equilibrium (time-independent) setups, as well as on situations in which electrons are isolated from their environments. Unfortunately, the assumption of equilibrium excludes a number of interesting technological applications, and the assumption of isolated electrons is often not realistic. Therefore, in order to develop useful topological devices that will benefit society, it is crucial to investigate how electrons in topological materials are affected by external perturbations and by their non-electronic environments. This investigation is indeed the prime objective of my research program.