Observation of Resonance of Kagome Flat Band Doublet

TL;DR

This study provides direct spectroscopic evidence of flat band resonance in a kagome bilayer material, revealing its coupling with dispersive bands and correlation with magnetic properties, advancing understanding of quantum states in kagome lattices.

Contribution

First direct observation of flat band resonance in a kagome lattice, linking it to magnetic correlations and demonstrating its unconventional nature.

Findings

Flat and dispersive bands show enhanced hybridization upon cooling.

Flat band resonance coincides with onset of antiferromagnetic correlations.

Spectroscopic evidence of flat band resonance in kagome material.

Abstract

The interplay between local and itinerant electrons underpins many correlated and topological quantum states. Kagome lattices provide an ideal platform by hosting both flat (localized states) and dispersive bands (itinerant states), yet direct spectroscopic evidence of their dynamical coupling has remained elusive. Here we report the long-sought flat band resonance in the quasi-two-dimensional kagome bilayer material CsCr6Sb6. Using angle-resolved photoemission spectroscopy, transport measurements, and combined density functional theory and dynamical mean-field theory, we identify coexisting flat band doublets and dispersive bands near the Fermi energy. Upon cooling, the flat and dispersive bands exhibit a pronounced enhancement of spectral weight and hybridization, directly evidencing flat band resonance. Crucially, this emergence coincides with the onset of short-range antiferromagnetic correlations, contrasting sharply with conventional Kondo lattice behavior. Our findings demonstrate not only the long-sought flat band resonance in kagome materials, but also its unconventional correlation with magnetism.