Massive Dirac fermions in a ferromagnetic kagome metal (1709.10007v1)

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.

• The paper demonstrates the experimental discovery of massive Dirac fermions in Fe₃Sn₂'s bilayer kagome lattice using ARPES.
• The methodology confirms a 30 meV mass gap and robust anomalous Hall conductivity above room temperature.
• The findings validate theoretical predictions on topological phases, paving the way for high-temperature quantum anomalous Hall devices.

Massive Dirac Fermions in a Ferromagnetic Kagome Metal

The paper "Massive Dirac fermions in a ferromagnetic kagome metal" explores the intriguing electronic structure in systems based on the kagome lattice, focusing on the ferromagnetic compound Fe$_{3}$Sn$_{2}$. The paper provides new insights into the topological electronic properties driven by the kagome lattice's inherent geometrical and symmetry characteristics, particularly when influenced by ferromagnetic order and spin-orbit coupling.

Key Findings

Fe$_{3}$Sn$_{2}$ features a bilayer kagome lattice structure, where the presence of massive Dirac fermions is demonstrated through angle-resolved photoemission spectroscopy (ARPES). The observed quasi-two-dimensional Dirac cones, located near the Fermi level, exhibit a mass gap of approximately 30 meV—a pivotal result showing the real-world manifestation of theoretical predictions about kagome systems.

The paper reports an anomalous Hall conductivity that remains robust above room temperature. This suggests significant Berry curvature effects due to broken time-reversal symmetry in these systems. The experimental observation of Dirac cones and their associated response is notably connected to the underlying symmetry of the kagome lattice and its inherent atomic spin-orbit interactions.

Implications and Theoretical Considerations

The implications of these findings are significant for the investigation of topological phases in condensed matter systems. By displaying that Fe$_{3}$Sn$_{2}$ can host Dirac fermions with a controllable mass via ferromagnetic and spin-orbit interactions, the paper sets a precedent for further exploration of kagome-based materials as potential candidates for realizing quantum anomalous Hall effects at higher temperatures than currently feasible.

Theoretically, this research contributes to understanding how lattice geometry and symmetry lead to exotic electronic states with potential applications in spintronics and quantum computing. The experimental results partly validate long-held theoretical models predicting topological phases due to kagome lattice structures, specifically under conditions where time-reversal symmetry is broken.

Future Directions

Future investigations could focus on fine-tuning the mass of Dirac fermions in kagome metals by varying ferromagnetic properties and spin-orbit coupling strengths. There is also prospect in exploring interactions in related compounds or engineering artificial kagome layers, potentially leading to devices harnessing these unique electronic characteristics for technological applications.

Furthermore, pursuing studies that examine the correlation effects and potential fractionalization in kagome systems may yield insights into fractional Chern insulators and the manifestation of other novel quantum states. The developments in fabrication of atomically thin kagome layers open pathways towards practical, room-temperature applications of the quantum anomalous Hall effect, with the potential for advancing next-generation electronic devices.

Overall, the paper provides an essential advancement in the experimental validation of kagome lattice-related phenomena, paving the way for new explorations into topological materials and their technological implementation.