Superconductivity provides access to the chiral magnetic effect of an unpaired Weyl cone

TL;DR

This paper demonstrates that superconductivity can enable the observation of the chiral magnetic effect in Weyl semimetals by selectively gapping out one Weyl cone, resulting in a measurable supercurrent response to magnetic fields.

Contribution

It introduces a flux bias method to gap out one Weyl cone in a superconductor, revealing the chiral magnetic effect as a supercurrent in equilibrium.

Findings

Superconductivity allows the chiral magnetic effect to be observed in equilibrium.

A flux bias gaps out one Weyl cone, leaving a single chiral Weyl fermion.

The supercurrent response is proportional to the magnetic field and chemical potential.

Abstract

The massless fermions of a Weyl semimetal come in two species of opposite chirality, in two cones of the band structure. As a consequence, the current $j$ induced in one Weyl cone by a magnetic field $B$ (the chiral magnetic effect, CME) is cancelled in equilibrium by an opposite current in the other cone. Here we show that superconductivity offers a way to avoid this cancellation, by means of a flux bias that gaps out a Weyl cone jointly with its particle-hole conjugate. The remaining gapless Weyl cone and its particle-hole conjugate represent a single fermionic species, with renormalized charge $e^\ast$ and a single chirality $\pm$ set by the sign of the flux bias. As a consequence, the CME is no longer cancelled in equilibrium but appears as a supercurrent response $\partial j/\partial B=\pm(e^\ast e/h^2)\mu$ along the magnetic field at chemical potential $\mu$.