Observation of Kondo lattice and Kondo-enhanced anomalous Hall effect in an itinerant ferromagnet

TL;DR

This study demonstrates the coexistence of Kondo lattice behavior and ferromagnetism in La$_{1-x}$Ce$_x$Co$_2$As$_2$, revealing enhanced anomalous Hall effects driven by topological features and hybridization effects.

Contribution

It provides the first comprehensive evidence of Kondo lattice formation with ferromagnetic order in an itinerant system and links topological Berry curvature to the anomalous Hall effect enhancement.

Findings

Observation of Kondo lattice state with ferromagnetism

Enhanced anomalous Hall effect correlated with Kondo regime

Identification of topological nodal rings contributing to Berry curvature

Abstract

The interplay between Kondo screening and magnetic interactions is central to comprehending the intricate phases in heavy-fermion compounds. However, the role of the itinerant magnetic order, which is driven by the conducting (c) electrons, has been largely uncharted in the context of heavy-fermion systems due to the scarcity of material candidates. Here we demonstrate the coexistence of the coherent Kondo screening and d-orbital ferromagnetism in material system La$_{1-x}$Ce$_x$Co$_2$As$_2$, through comprehensive thermodynamic and electrical transport measurements. Additionally, using angle-resolved photoemission spectroscopy (ARPES), we further observe the f-orbit-dominated bands near the Fermi level ($E_f$) and signatures of the f-c hybridization below the magnetic transition temperature, providing strong evidence of Kondo lattice state in the presence of ferromagnetic order. Remarkably, by changing the ratio of Ce/La, we observe a substantial enhancement of the anomalous Hall effect (AHE) in the Kondo lattice regime. The value of the Hall conductivity quantitatively matches with the first-principle calculation that optimized with our ARPES results and can be attributed to the large Berry curvature (BC) density engendered by the topological nodal rings composed of the Ce-4f and Co-3d orbitals at $E_f$. Our findings point to the realization of a new platform for exploring correlation-driven topological responses in a novel Kondo lattice environment.