Chiral Quasiparticles at the Fermi Surface of the Weyl Semimetal TaAs

TL;DR

This study maps the Fermi surface of TaAs, revealing chiral Weyl quasiparticles near the Fermi level, which are crucial for understanding its topological quantum phenomena.

Contribution

It provides the first detailed experimental evidence of Fermi surface pockets near Weyl points in TaAs, confirming the presence of chiral quasiparticles.

Findings

Identification of three types of Fermi surface pockets.

Two electron pockets are topologically non-trivial Weyl pockets.

One trivial hole pocket was also observed.

Abstract

Tantalum arsenide is a member of the non-centrosymmetric monopnictides, which are putative Weyl semimetals. In these materials, three-dimensional chiral massless quasiparticles, the so-called Weyl fermions, are predicted to induce novel quantum mechanical phenomena, such as the chiral anomaly and topological surface states. However, their chirality is only well-defined if the Fermi level is close enough to the Weyl points that separate Fermi surface pockets of opposite chirality exist. In this article, we present the bulk Fermi surface topology of high quality single crystals of TaAs, as determined by angle-dependent Shubnikov-de Haas and de Haas-van Alphen measurements combined with ab-initio band-structure calculations. Quantum oscillations originating from three different types of Fermi surface pocket were found in magnetization, magnetic torque, and mag- netoresistance measurements performed in magnetic fields up to 14 T and temperatures down to 1.8 K. Of these Fermi pockets, two are pairs of topologically non-trivial electron pockets around the Weyl points and one is a trivial hole pocket. Unlike the other members of the non-centrosymmetric monopnictides, TaAs is the first Weyl semimetal candidate with the Fermi energy suffciently close to both types of Weyl points to generate chiral quasiparticles at the Fermi surface.