Signatures of Kondo-lattice behavior in the two-dimensional ferromagnet Fe$_3$GeTe$_2$

TL;DR

This study uses scanning tunneling microscopy and spectroscopy at 1.1 K to reveal signatures of Kondo-lattice behavior in the two-dimensional ferromagnet Fe$_3$GeTe$_2$, highlighting the presence of a coherent Kondo lattice and its robustness.

Contribution

It provides direct experimental evidence of Kondo-lattice signatures in Fe$_3$GeTe$_2$, a 2D ferromagnet, through surface spectroscopy revealing hybridization and a small energy gap.

Findings

Observation of a spatially varying Fano lineshape indicating Kondo resonance.

Identification of a small gap (~5 meV) suggesting a coherent Kondo lattice.

Robustness of Kondo correlations against magnetic adatoms.

Abstract

Fe$_2$GeTe$_3$ is a paradigmatic van der Waals magnet with the full microscopic picture of magnetic interactions still under debate. Here, we use scanning tunneling microscopy and spectroscopy at 1.1 K to map out the low-energy physics on the surface. In agreement with previous works, we observe a spatially varying Fano lineshape that has been ascribed to a Kondo resonance. In addition, we identify a small gap of $\approx$ 5 meV width on top of the larger-energy Fano resonance. We suggest that this gap is the signature of a coherent Kondo lattice that has been proposed to originate from hybridization of a strongly dispersing and a flat band both derived from $d$ electrons of the Fe atoms in the lattice. Adding magnetic adatoms on the surface hardly influences the magnetic signatures of the substrate, indicating the robustness of the intralayer Kondo correlations against magnetic adsorbates.