Coexistence of Weyl Physics and Planar Defects in Semimetals TaP and TaAs

TL;DR

This study investigates the structural defects in Weyl semimetals TaP and TaAs, demonstrating that despite high defect densities, key quantum properties like Weyl fermions and quantum oscillations remain robust, indicating their resilience in real-world crystals.

Contribution

It provides new insights into how defects and non-stoichiometry affect the electronic structure and Weyl physics in TaP and TaAs semimetals.

Findings

Quantum oscillations observed in defective TaP crystals.

Weyl pockets remain near the Fermi surface despite stacking faults.

Defects do not significantly impair Weyl fermion-related phenomena.

Abstract

We report a structural study of the Weyl semimetals TaAs and TaP, utilizing diffraction and imaging techniques, where we show that they contain a high density of defects, leading to non-stoichiometric single crystals of both semimetals. Despite the observed defects and non-stoichiometry on samples grown using techniques already reported in the literature, de Haas-van Alphen measurements on TaP reveal quantum oscillations and a high carrier mobility, an indication that the crystals are of quality comparable to those reported elsewhere. Electronic structure calculations on TaAs reveal that the position of the Weyl points relative to the Fermi level shift with the introduction of vacancies and stacking faults. In the case of vacancies the Fermi surface becomes considerably altered, while the effect of stacking faults on the electronic structure is to allow the Weyl pockets to remain close to the Fermi surface. The observation of quantum oscillations in a non-stoichiometric crystal and the persistence of Weyl fermion pockets near the Fermi surface in a crystal with stacking faults point to the robustness of these quantum phenomena in these materials.