When Symmetries Twist: Anomaly Inflow on Monodromy Defects

TL;DR

This paper investigates the properties of monodromy defects in topological phases and anomalous theories, revealing their role in hosting protected edge modes and facilitating adiabatic charge pumping.

Contribution

It introduces a framework for understanding monodromy defects as domain walls influenced by anomalies, with new insights into their topological and gapless features.

Findings

Monodromy defects host protected chiral edge modes.

Localized flux induces topological order and anomaly inflow.

Defects enable adiabatic pumping of gapless modes.

Abstract

Monodromy defects describe a dynamical termination of topological symmetry operators, and are sourced by a localized background magnetic flux. We study their properties in gapped SPT phases and, by inflow, in gapless theories with an anomalous symmetry. The background flux acts as a source for the anomaly, impacting the definition of the monodromy defect, which can only be defined as a domain wall between the symmetry generator and a topological order induced by the anomaly. The topological dressing has several consequences, such as the presence of protected chiral edge modes on the defect's worldvolume, and the adiabatic pumping of gapless degrees of freedom bound to the localized flux. We verify our predictions in several examples, focusing on monodromy defects for anomalous chiral symmetries, both in the continuum and on the lattice.