Massive Dirac fermions in a ferromagnetic kagome metal

TL;DR

This paper reports the discovery of massive Dirac fermions in a ferromagnetic kagome metal, revealing topological electronic properties and Berry curvature effects in a correlated electron system, with potential implications for quantum topological phases.

Contribution

First experimental evidence of a ferromagnetic kagome metal supporting massive Dirac fermions and topological electronic states in a correlated electron system.

Findings

Observation of quasi-2D Dirac cones near the Fermi level with a 30 meV mass gap.

Detection of temperature-independent anomalous Hall conductivity above room temperature.

Identification of symmetry-driven topological electronic properties in a ferromagnetic kagome lattice.

Abstract

The kagome lattice is a two-dimensional network of corner-sharing triangles known as a platform for exotic quantum magnetic states. Theoretical work has predicted that the kagome lattice may also host Dirac electronic states that could lead to topological and Chern insulating phases, but these have evaded experimental detection to date. Here we study the d-electron kagome metal Fe$_3$Sn$_2$ designed to support bulk massive Dirac fermions in the presence of ferromagnetic order. We observe a temperature independent intrinsic anomalous Hall conductivity persisting above room temperature suggestive of prominent Berry curvature from the time-reversal breaking electronic bands of the kagome plane. Using angle-resolved photoemission, we discover a pair of quasi-2D Dirac cones near the Fermi level with a 30 meV mass gap that accounts for the Berry curvature-induced Hall conductivity. We show this behavior is a consequence of the underlying symmetry properties of the bilayer kagome lattice in the ferromagnetic state with atomic spin-orbit coupling. This report provides the first evidence for a ferromagnetic kagome metal and an example of emergent topological electronic properties in a correlated electron system. This offers insight into recent discoveries of exotic electronic behavior in kagome lattice antiferromagnets and may provide a stepping stone toward lattice model realizations of fractional topological quantum states.