Chiral separation effect for spin 3/2 fermions

TL;DR

This paper investigates the Chiral Separation Effect (CSE) in systems with spin 3/2 fermions, revealing significantly enhanced CSE conductivity and establishing a topological relation between CSE and Chern numbers in topological semimetals.

Contribution

It demonstrates that CSE conductivity for spin 3/2 fermions is substantially larger than for Dirac or Weyl fermions and proves a topological index theorem linking CSE to Chern numbers.

Findings

CSE conductivity is five times larger for RSA model than for Dirac fermions.

CSE conductivity is four times larger in Rarita-Schwinger-Weyl semimetals than in Weyl fermions.

CSE conductivity is proportional to the Chern number and is topologically protected.

Abstract

Chiral Separation Effect (CSE) for systems that feature spin 3/2 fermions was considered. For the self-consistent Adler's model with relativistic massless Rarita-Schwinger fermions (RSA model), we found that the CSE conductivity is five times larger than for massless Dirac fermions. For a model of four-fold band crossing in Rarita-Schwinger-Weyl semimetals, in which massless fermions with quasispin 3/2 exist, we calculated that the CSE conductivity is four times larger than for Weyl fermions. We show that CSE conductivity for any multi-degenerate Fermi point in topological semimetals is proportional to its Chern number and is topologically protected. Along the calculations, we proved an index theorem that relates Chern number of a Fermi-point and spectral asymmetry of the corresponding Landau band structure. The assumption that CSE for any system of chiral fermions is dictated by the corresponding Chern number is found to be correct for RSA model (and for the Dirac fermions).