Criteria for directly detecting topological Fermi arcs in Weyl semimetals

TL;DR

This paper establishes criteria for directly identifying topological Fermi arcs in Weyl semimetals using ARPES, demonstrating their application to TaAs and NbP, and providing a rigorous topological characterization of TaAs.

Contribution

It introduces experimentally accessible conditions to confirm Fermi arcs in Weyl semimetals without heavy reliance on calculations, and rigorously demonstrates a non-zero Chern number in TaAs.

Findings

Confirmed Fermi arcs in TaAs via ARPES and topological criteria.

Demonstrated a non-zero Chern number in TaAs by counting chiral edge modes.

Showed that Fermi arcs in NbP are difficult to observe with current ARPES resolution.

Abstract

The recent discovery of the first Weyl semimetal in TaAs provides the first observation of a Weyl fermion in nature and demonstrates a novel type of anomalous surface state, the Fermi arc. Like topological insulators, the bulk topological invariants of a Weyl semimetal are uniquely fixed by the surface states of a bulk sample. Here, we present a set of distinct conditions, accessible by angle-resolved photoemission spectroscopy (ARPES), each of which demonstrates topological Fermi arcs in a surface state band structure, with minimal reliance on calculation. We apply these results to TaAs and NbP. For the first time, we rigorously demonstrate a non-zero Chern number in TaAs by counting chiral edge modes on a closed loop. We further show that it is unreasonable to directly observe Fermi arcs in NbP by ARPES within available experimental resolution and spectral linewidth. Our results are general and apply to any new material to demonstrate a Weyl semimetal.