Torsion-induced chiral magnetic current in equilibrium

TL;DR

This paper investigates how torsion in spacetime can induce equilibrium chiral magnetic currents in Dirac and Weyl semimetals, revealing conditions under which such currents appear or vanish, with implications for condensed matter systems.

Contribution

It provides a detailed calculation of torsion-induced currents in Dirac fermions, highlighting the conditions for their emergence and contrasting with previous theoretical predictions.

Findings

Torsion can induce a local equilibrium current similar to the chiral magnetic effect.

The current induced by torsion vanishes when considering Weyl node separation.

Condensed matter systems with screw dislocations can realize torsion effects.

Abstract

We study equilibrium transport properties of massless Dirac fermions at finite temperature and chemical potential in spacetime accompanied by torsion, which in four dimensions couples with Dirac fermions as an axial gauge field. In particular, we compute the current density at the linear order in the torsion as well as in an external magnetic field with the Pauli-Villars regularization, finding that an equilibrium current akin to the chiral magnetic current is locally induced. Such torsion can be realized in condensed matter systems along a screw dislocation line, around which localized and extended current distributions are predicted so as to be relevant to Dirac and Weyl semimetals. Furthermore, we compute the current density at the linear order in the torsion as well as in a Weyl node separation, which turns out to vanish in spite of being allowed from the symmetry perspective. Contrasts of our findings with torsion-induced currents from previous work are also discussed.