Severe violation of the Wiedemann-Franz law in quantum oscillations of NbP

TL;DR

This study reveals a significant violation of the Wiedemann-Franz law in NbP, where quantum oscillations in thermal conductivity are much larger than expected, suggesting novel chiral zero sound effects in Weyl semimetals.

Contribution

The paper demonstrates a large deviation from the Wiedemann-Franz law in NbP's quantum oscillations, highlighting potential chiral zero sound as a new thermal transport mechanism.

Findings

Quantum oscillations in thermal conductivity are two orders of magnitude larger than predicted.

Oscillation frequencies match those from the electron pocket near Weyl nodes.

Chiral zero sound may explain the observed violation of the Wiedemann-Franz law.

Abstract

The thermal conductivity (k) of the Weyl semimetal NbP was studied with the thermal gradient and magnetic field applied parallel to [0 0 1] direction. At low temperatures k(B) exhibits large quantum oscillations with frequencies matching two of several determined from the Shubnikov - de Haas effect measured on the same sample with analogous electrical current and magnetic field orientation. Both frequencies found in k(B) originate from the electron pocket enclosing a pair of Weyl nodes. The amplitude of the oscillatory component of the thermal conductivity turns out to be two orders of magnitude larger than the corresponding value calculated from the electrical conductivity using the Wiedemann - Franz law. Analysis of possible sources of this discrepancy indicates the chiral zero sound effect as a potential cause of its appearance.