Modern electronics is built on semiconductors, whose utility comes from their ability to operate on either side of the conductor-insulator dichotomy. For practical applications, however, semiconductors face certain unavoidable limitations imposed by the physics of Anderson localization and by the disorder introduced through doping. In this talk I discuss whether these same limitations apply to nodal semimetals, which are a novel class of three-dimensional materials that have a vanishing density of states (like insulators) but no gap to electron-hole excitations (like conductors). I show that, surprisingly, in a certain class of nodal semimetals the electronic mobility can far exceed the bounds that constrain doped semiconductors, becoming divergingly large even with a finite concentration of charged impurities. I then discuss the thermoelectric effect in semimetals, and show that their electron-hole symmetry allows for a thermopower that grows without bound under the application of a strong magnetic field. This large thermopower apparently enables the development of devices with record-large thermoelectric figure of merit.
Semimetals Unlimited: Unbounded electrical and thermal transport properties in three-dimensional nodal semimetals