Negative magnetoresistance without well-defined chirality in the Weyl semimetal TaP

TL;DR

This study investigates the negative magnetoresistance in the Weyl semimetal TaP, showing it occurs even without well-defined chirality, and highlights the importance of Fermi surface topology and experimental conditions in observing the chiral magnetic effect.

Contribution

The paper provides detailed Fermi surface topology of TaP and demonstrates negative magnetoresistance without well-defined Weyl nodes, clarifying conditions for the chiral magnetic effect.

Findings

Negative magnetoresistance observed in TaP despite ill-defined chirality.

Fermi surface consists of spin-polarized banana-shaped pockets near Weyl points.

Current inhomogeneity can influence magnetoresistance measurements.

Abstract

Weyl semimetals (WSMs) are topological quantum states wherein the electronic bands linearly disperse around pairs of nodes, the Weyl points, of fixed (left or right) chirality. The recent discovery of WSM materials triggered an experimental search for the exotic quantum phenomenon known as the chiral anomaly. Via the chiral anomaly nonorthogonal electric and magnetic fields induce a chiral density imbalance that results in an unconventional negative longitudinal magnetoresistance, the chiral magnetic effect. Recent theoretical work suggests that this effect does not require well-defined Weyl nodes. Experimentally however, it remains an open question to what extent it survives when chirality is not well-defined, for example when the Fermi energy is far away from the Weyl points. Here, we establish the detailed Fermi surface topology of the recently identified WSM TaP via a combination of angle-resolved quantum oscillation spectra and band structure calculations. The Fermi surface forms spin-polarized banana-shaped electron and hole pockets attached to pairs of Weyl points. Although the chiral anomaly is therefore ill-defined, we observe a large negative magnetoresistance (NMR) appearing for collinear magnetic and electric fields as observed in other WSMs. In addition, we show experimental signatures indicating that such longitudinal magnetoresistance measurements can be affected by an inhomogeneous current distribution inside the sample in a magnetic field. Our results provide a clear framework how to detect the chiral magnetic effect.