Room-Temperature Ferromagnetic Topological Phase in CrO$_{2}$: From Tripe Fermions to Weyl Fermions

TL;DR

This paper predicts that rutile CrO$_{2}$, a common ferromagnetic material, hosts topologically nontrivial fermions at room temperature, including Weyl points, which could enable new topological applications.

Contribution

The study reveals that rutile CrO$_{2}$ exhibits ferromagnetic topological features, including triple nodal points and Weyl fermions, confirmed through first-principles calculations and symmetry analysis.

Findings

Rutile CrO$_{2}$ hosts triple nodal points without SOC.

SOC splits triple nodal points into Weyl points on the magnetic axis.

Fermi arcs and quasiparticle interference patterns are observable.

Abstract

Ferromagnetic topological semimetals due to their band topology co-existing with intrinsic magnetization exerted important influences on early study of topological fermions. However, they have not been observed in experiments up to now. In this work, we propose that rutile CrO$_{2}$, a widely used half-metallic ferromagnetic material in magnetic recording taps, exhibits unexpected ferromagnetic topological features. Using first-principles calculations and symmetry analysis, we reveal that rutile CrO$_2$ hosts the triple nodal points in the absence of spin orbital coupling (SOC). By taking into account of SOC, each triple nodal point splits into two Weyl points, which are located on the magnetic axis with four-fold rotational symmetry. Notably, the Fermi arcs and accompanying quasiparticle interference patterns are clearly visible, which facilitate experimental observations. In addition, we find that another experimentally synthesized CrO$_{2}$ in CaCl$_2$ structure, also hosts the topologically nontrivial ferromagnetic phase. Our findings substantially advance the experimental realization of ferromagnetic topological semimetals. More importantly, room-temperature time-reversal-breaking Weyl fermions in CrO$_{2}$ may result in promising applications related to the topological phenomena in industry.