Magnetic tunneling induced Weyl node annihilation in TaP

TL;DR

This paper demonstrates magnetic field-induced Weyl node annihilation in TaP, revealing the nontrivial topology of Weyl fermions through high-field transport measurements and Landau level analysis.

Contribution

It provides the first experimental evidence of Weyl node annihilation driven by magnetic coupling in a Weyl semimetal, specifically in TaP.

Findings

Sharp Hall resistivity sign reversal at specific magnetic field

W1 Weyl node separation leads to Landau level crossing

No annihilation observed for W2 Weyl nodes due to larger separation

Abstract

Weyl nodes are topological objects in three-dimensional metals. Their topological property can be revealed by studying the high-field transport properties of a Weyl semimetal. While the energy of the lowest Landau band (LLB) of a conventional Fermi pocket always increases with magnetic field due to the zero point energy, the LLB of Weyl cones remains at zero energy unless a strong magnetic field couples the Weyl fermions of opposite chirality. In the Weyl semimetal TaP, we achieve such a magnetic coupling between the electron-like Fermi pockets arising from the W1 Weyl fermions. As a result, their LLBs move above chemical potential, leading to a sharp sign reversal in the Hall resistivity at a specific magnetic field corresponding to the W1 Weyl node separation. By contrast, despite having almost identical carrier density, the annihilation is unobserved for the hole-like pockets because the W2 Weyl nodes are much further separated. These key findings, corroborated by other systematic analyses, reveal the nontrivial topology of Weyl fermions in high-field measurements.