Callan-Rubakov effects in topological insulators

TL;DR

This paper demonstrates a defect-induced quantum anomaly in topological insulators, where localized states at dislocations or fluxes mimic magnetic impurities, revealing a condensed-matter analog of the Callan-Rubakov effect.

Contribution

It introduces a novel defect-catalyzed quantum anomaly in topological insulators, extending the Callan-Rubakov effect to condensed matter systems with topological classification.

Findings

Localized states at dislocations mediate spin-flip scattering.

Non-Hermitian topological number guarantees state robustness.

Generalization to other topological materials using K-theory.

Abstract

The Callan-Rubakov effect describes monopole-catalyzed proton decay. While this effect is fundamental for quantum field theories, its experimental observation has remained far from reality. Here, we reveal a similar, but experimentally reachable, defect-catalysis of the quantum anomaly in topological materials. In particular, surface Dirac fermions on topological insulators develop a distinct localized state at the position of dislocations or $\pi$-fluxes, which mediates spin-flip time-reversal breaking scattering or absorption of electrons. Despite the Hermiticity of topological insulators, a non-Hermitian topological number guarantees the robust existence of the localized state. Our finding implies that non-magnetic defects may behave like magnetic impurities on surfaces of topological insulators. Using the K-theory classification, we generalize this condensed-matter version of the Callan-Rubakov effect to other classes of topological materials.