Axion electrodynamics of Weyl superconductors with broken time-reversal symmetry
Vira Shyta, Jeroen van den Brink, Flavio S. Nogueira
TL;DR
This work investigates axion electrodynamics in Weyl semimetals with broken time-reversal symmetry and its realization in Weyl superconductors within the London regime. By formulating an Abelian Higgs model with an axion term and a TRB axion field $a(\mathbf{r})=\mathbf{b}\cdot\mathbf{r}$, it demonstrates a topological mass generation for photons, yielding a gapped branch $E_+(p)$ in the spectrum and a gapless mode $E_-(p)$. In the superconducting state, the axion term couples electric and magnetic fields, producing coupled Meissner screening with two decay lengths, induced transverse electric fields, and a nonzero electromagnetic angular momentum $L_z^{\mathrm{EM}}$; vortex solutions further exhibit axion-induced electric fields and an angular momentum tied to flux quantization. The results reveal a rich interplay between topological magnetoelectric effects and conventional superconducting screening, with potential experimental signatures via angular momentum measurements and rotation-induced responses.
Abstract
The low-energy effective description of Weyl semimetals is defined by the axion electrodynamics, which captures the effects arising due to the presence of nodes of opposite chirality in the electronic structure. Here we explore the magnetoelectric response of time-reversal breaking (TRB) Weyl superconductors in the London regime. The influence of the axion contribution leads to an increase in the London penetration depth$-$a behavior that can be anticipated by first considering the photon spectrum of a TRB Weyl semimetal. Moreover, we find that both the Meissner state and the vortex phase feature an interplay between the electric and magnetic fields. This leads to a nonvanishing electromagnetic angular momentum, which we calculate for a number of geometrical configurations.