Joel Moore, Department of Physics, University of California, Berkeley, and Materials Sciences Division, Lawrence Berkeley Laboratory
Much of condensed matter physics is concerned with understanding how different kinds of order emerge from interactions between a large number of simple constituents. In ordered phases such as crystals, magnets, and superfluids, the order is understood through "symmetry breaking": in a crystal, for example, the continuous symmetries of space under rotations and translations are not reflected in the ground state. A major discovery of the 1980s was that electrons confined to two dimensions and in a strong magnetic field exhibit a completely different, topological type of order that underlies the quantum Hall effect.
Topological order was recently discovered following theoretical predictions in some three-dimensional materials, dubbed "topological insulators", in zero magnetic field. Spin-orbit coupling, an intrinsic property of all solids, drives the formation of the topological state. This talk will explain what topological order means, how topological insulators were predicted and discovered, and how they realize the "axion electrodynamics" studied by particle physicists in the 1980s. Connections to other fields and possible applications of these new materials are discussed in closing.