Gauge invariance and anomalies in condensed matter physics

Abstract

This paper begins with a summary of a powerful formalism for the study of electronic states in condensed matter physics called “gauge theory of states/phases of matter.” The chiral anomaly, which plays quite a prominent role in that formalism, is recalled. I then sketch an application of the chiral anomaly in 1 + 1 dimensions to quantum wires. Subsequently, some elements of the quantum Hall effect in two-dimensional (2D) gapped (“incompressible”) electron liquids are reviewed. In particular, I discuss the role of anomalous chiral edge currents and of the anomaly inflow in 2D gapped electron liquids with explicitly or spontaneously broken time reversal, i.e., in Hall and Chern insulators. The topological Chern–Simons action yielding transport equations valid in the bulk of such systems and the associated anomalous edge action are derived. The results of a general classification of “Abelian” Hall insulators are outlined. After some remarks on induced Chern–Simons actions, I sketch results on certain 2D chiral photonic wave guides. I then continue with an analysis of chiral edge spin-currents and bulk response equations in time-reversal invariant 2D topological insulators of electron gases with spin–orbit interactions. The “chiral magnetic effect” in 3D systems and axion-electrodynamics are reviewed next. This prepares the ground for an outline of a general theory of 3D topological insulators, including “axionic insulators.” Some remarks on Weyl semi-metals, which exhibit the chiral magnetic effect, and on Mott transitions in 3D systems with dynamical axion-like degrees of freedom conclude this review.