Chiral anomaly, Charge Density Waves, and Axion Strings from Weyl Semimetals

TL;DR

This paper explores how Weyl semimetals can develop charge density waves and axion strings through chiral symmetry breaking, revealing new topological phenomena with potential implications for dissipationless transport.

Contribution

It demonstrates the emergence of axion insulators and axion strings as dislocations in charge density waves in Weyl semimetals, linking topological defects to observable electronic properties.

Findings

Charge density waves arise from chiral symmetry breaking in Weyl semimetals.

Axion strings are realized as dislocations in charge density waves.

Axion strings support gapless chiral modes, affecting transport properties.

Abstract

We study dynamical instability and chiral symmetry breaking in three dimensional Weyl semimetals, which turns Weyl semimetals into "axion insulators". Charge density waves (CDW) is found to be the natural consequence of the chiral symmetry breaking. The phase mode of this charge density wave state is identified as the axion, which couples to electromagnetic field in the topological $\theta{\bf E}\cdot{\bf B}$ term. One of our main results is that the "axion strings" can be realized as the (screw or edge) dislocations in the charge density wave, which provides a simple physical picture for the elusive axion strings. These axion strings carry gapless chiral modes, therefore they have important implications for dissipationless transport properties of Weyl semimetals with broken symmetry.