Observation of Weyl nodes in robust type-II Weyl semimetal WP2

TL;DR

This study provides direct experimental evidence of tilted Weyl cone bands in WP2, confirming its status as a robust type-II Weyl semimetal and elucidating the origin of surface Fermi arcs and related transport phenomena.

Contribution

It demonstrates the direct observation of tilted Weyl cones in WP2 using ARPES and first-principles calculations, clarifying the origin of Weyl nodes and surface states in this material.

Findings

Weyl nodes in WP2 originate from splitting of degenerate bands due to spin-orbit coupling.

Weyl cones are tilted, confirming type-II Weyl semimetal nature.

Weyl nodes have Chern numbers C = ±2, unique among WSMs.

Abstract

Distinct to type-I Weyl semimetals (WSMs) that host quasiparticles described by the Weyl equation, the energy dispersion of quasiparticles in type-II WSMs violates Lorentz invariance and the Weyl cones in the momentum space are tilted. Since it was proposed that type-II Weyl fermions could emerge from (W,Mo)Te2 and (W,Mo)P2 families of materials, a large numbers of experiments have been dedicated to unveil the possible manifestation of type-II WSM, e.g. the surface-state Fermi arcs. However, the interpretations of the experimental results are very controversial. Here, using angle-resolved photoemission spectroscopy supported by the first-principles calculations, we probe the tilted Weyl cone bands in the bulk electronic structure of WP2 directly, which are at the origin of Fermi arcs at the surfaces and transport properties related to the chiral anomaly in type-II WSMs. Our results ascertain that due to the spin-orbit coupling the Weyl nodes originate from the splitting of 4-fold degenerate band-crossing points with Chern numbers C = $\pm$2 induced by the crystal symmetries of WP2, which is unique among all the discovered WSMs. Our finding also provides a guiding line to observe the chiral anomaly which could manifest in novel transport properties.