Detection of relativistic fermions in Weyl semimetal TaAs by magnetostriction measurements

TL;DR

This study demonstrates that magnetostriction measurements in TaAs can reveal the presence of Weyl fermions, with a linear-in-field magnetostriction component serving as a key signature of these relativistic particles.

Contribution

The paper introduces a novel magnetostriction-based method to detect Weyl fermions in topological semimetals, supported by theoretical modeling and experimental data.

Findings

Large $c$-axis magnetostriction in TaAs

Strong angular dependence of $a$-axis magnetostriction

Linear-in-field magnetostriction above the ultra-quantum limit

Abstract

Thus far, a detection of the Dirac or Weyl fermions in topological semimetals remains often elusive, since in these materials conventional charge carriers exist as well. Here, measuring a field-induced length change of the prototype Weyl semimetal TaAs at low temperatures, we find that its $c$-axis magnetostriction amounts to relatively large values whereas the $a$-axis magnetostriction exhibits strong variations with changing the orientation of the applied magnetic field. It is discovered that at magnetic fields above the ultra-quantum limit, the magnetostriction of TaAs contains a linear-in-field term, which, as we show, is a hallmark of the Weyl fermions in a material. Developing a theory for the magnetostriction of noncentrosymmetric topological semimetals and applying it to TaAs, we additionally find several parameters characterizing the interaction between the relativistic fermions and elastic degrees of freedom in this semimetal. Our study shows how dilatometry can be used to unveil Weyl fermions in candidate topological semimetals.