Helical Separation Effect and helical heat transport for Dirac fermions

TL;DR

This paper introduces the Helical Separation Effect, a novel dissipationless helicity current in massless fermions under magnetic fields, and explores related heat transport phenomena in neutral plasmas.

Contribution

It presents the first theoretical demonstration of the Helical Separation Effect and the Helical Magnetic Heat Effect in Dirac fermions, expanding understanding of helicity transport.

Findings

Helical current flows along magnetic fields in neutral plasmas.

Heat flux of Dirac fermions is generated by the Helical Magnetic Heat Effect.

Possible hydrodynamic modes related to HSE are discussed.

Abstract

An ensemble of massless fermions can be characterized by its total helicity charge given by the sum of axial charges of particles minus the sum of axial charges of antiparticles. We show that charged massless fermions develop a dissipationless flow of helicity along the background magnetic field. We dub this transport phenomenon as the Helical Separation Effect (HSE). Contrary to its chiral cousin, the Chiral Separation Effect, the HSE produces the helical current in a neutral plasma in which all chemical potentials vanish. In addition, we uncover the Helical Magnetic Heat Effect which generates a heat flux of Dirac fermions along the magnetic field in the presence of non-vanishing helical charge density. We also discuss possible hydrodynamic modes associated with the HSE in neutral plasma.