Nonequilibrium and dissipative effects in topological materials

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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.