Extra Seminar - Würzburg ToCoTronics Colloquium

Metals and Insulators are reasonably well understood but very different states of matter. Most interesting materials, however, are obtaining by introducing few carriers in insulators, and the action takes place in the metal-insulator transition region. Here the electrons move slowly as they barely conduct, and they interact strongly, displaying unfamiliar quantum dynamics which are difficult to understand. In this Colloquium, we shall give a board overview of the key physical concepts that describe this regime, and discuss modern theoretical methods which prove capable to capture many of the puzzling phenomena. Examples will be given of several new experimental plaforms, ranging from two-dimensional electron liquids in semiconductors, to organic molecular solids, and the recently discovered “moiré” bilayer devices. In all these systems, narrow electronic bands can be engineered and fine-tuned to access the strong-coupling regime, revealing remarkable universality across the metal-insulator quantum critical region. These discoveries suggest that soon we’ll be able to design and fabricate “materials by design”, with properties that can be hand-tailored to the needs of modern quantum information technology.