Chiral symmetry breaking and violation of the Wiedemann-Franz law in underdoped cuprates

TL;DR

This paper explains the violation of the Wiedemann-Franz law in underdoped cuprates through spin-charge separation and chiral symmetry breaking, leading to a fermion mass gap that affects thermal conductivity.

Contribution

It introduces a theoretical model involving dynamical chiral symmetry breaking in a (2+1)-D system to explain experimental anomalies in underdoped cuprates.

Findings

Fermion mass gap suppresses residual thermal conductivity.

Violation of Wiedemann-Franz law explained by spin-charge separation.

Physical implications of chiral symmetry breaking discussed.

Abstract

We propose that the recently observed violation of the Wiedemann-Franz law in the normal state of underdoped cuprates is caused by spin-charge separation and dynamical chiral symmetry breaking in a (2+1)-dimensional system consisting of massless Dirac fermions, charged bosons and a gauge field. While the d-wave spinon gap vanishes at the Fermi points, the nodal fermions acquire a finite mass due to strong gauge fluctuations. This mass provides a gap below which no free fermions can be excited. This implies that there is not a residual linear term for the thermal conductivity, in good agreement with experiments. Other physical implications of the CSB are also discussed.