Massive Dirac fermions in a ferromagnetic kagome metal

Abstract

The kagome lattice is a two-dimensional network of corner-sharing triangles that is known to host exotic quantum magnetic states. Theoretical work has predicted that kagome lattices may also host Dirac electronic states that could lead to topological and Chern insulating phases, but these states have so far not been detected in experiments. Here we study the d-electron kagome metal FeSn, which is designed to support bulk massive Dirac fermions in the presence of ferromagnetic order. We observe a temperature-independent intrinsic anomalous Hall conductivity that persists above room temperature, which is suggestive of prominent Berry curvature from the time-reversal-symmetry-breaking electronic bands of the kagome plane. Using angle-resolved photoemission spectroscopy, we observe a pair of quasi-two-dimensional Dirac cones near the Fermi level with a mass gap of 30 millielectronvolts, which correspond to massive Dirac fermions that generate Berry-curvature-induced Hall conductivity. We show that this behaviour is a consequence of the underlying symmetry properties of the bilayer kagome lattice in the ferromagnetic state and the atomic spin-orbit coupling. This work provides evidence for a ferromagnetic kagome metal and an example of emergent topological electronic properties in a correlated electron system. Our results provide insight into the recent discoveries of exotic electronic behaviour in kagome-lattice antiferromagnets and may enable lattice-model realizations of fractional topological quantum states.

Large anomalous Hall effect in the chiral-lattice antiferromagnet CoNb3S6

“…Here, the anomalous Hall effect has been attributed to the combined effect of non-collinear antiferromagnetic spin texture and electronic band structure 12,13 . A large anomalous Hall coefficient, reported for Fe 3 Sn 2 15,16 cannot be described by the ferromagnetic component alone and is believed to be due to the massive quasi-2D Dirac cones near the Fermi energy. Likewise, the large AHE observed in frustrated systems such as Pr 2 Ir 2 O 7 has been attributed to the non-coplanar spin texture 27 .…”

“…Reformulation of the SOC-induced intrinsic mechanism of AHE in ferromagnets to the Berry phase curvature in momentum space has been fruitful in predicting and describing the AHE in several other systems, including Weyl (semi)metals 3 , non-collinear antiferromagnets 4 , non-coplanar magnets 5–7 , and other nontrivial spin textures 8–11 . Recent observations of the large anomalous Hall effect in metals with possible Weyl 12–14 and massive Dirac fermions 15,16 and/or complex spin textures, e.g., skyrmion bubbles 17 , have generated interest in such materials, especially for the role of correlated topological states in the emergent electronic properties. Here we present a large AHE in CoNb 3 S 6 that cannot be understood in terms of conventional mechanisms of the AHE.…”

Symmetry‐Based Electron–Phonon Decoupling and Jahn–Teller Theorem Violation in Specific Crystalline Structures

“…It turns out that such systems are already in the focus of intensive scientific research because of their exceptional properties. Let us mention just a few: carbyne, a material stronger than graphene, Kagome lattices, interesting for their exotic topological states, and copper‐oxide planes relevant for high‐temperature superconductivity.…”

Implementation of non-collinear spin-constrained DFT calculations in SIESTA with a fully relativistic Hamiltonian

“…We have used the CDFT formalism to study possible metastable frustrated magnetic states of a V 4+ kagome slab by comparison of the total SC energy between different states. The kagome lattice is a two-dimensional network of corner-sharing triangles that is known to host exotic quantum magnetic states [30]. figure 2(A) shows a scheme of the V atoms arrangement in the kagome structure).…”