Correlated Electronic Structure and Incipient Flat Bands of the Kagome Superconductor CsCr3Sb5

TL;DR

This study investigates the electronic structure of the kagome superconductor CsCr3Sb5, revealing incipient flat bands, strong correlations, and weak magnetic-electronic interplay, advancing understanding of its unconventional properties.

Contribution

It provides the first detailed experimental and theoretical analysis of CsCr3Sb5's electronic structure, highlighting flat bands and strong correlations distinct from related compounds.

Findings

Incoherent Cr 3d orbitals contribute to flat bands near the Fermi level.

Weak change in electronic structure across the magnetic transition at 55 K.

Enhanced electron scattering rate correlates with magnetic transition and transport properties.

Abstract

Kagome materials exhibit many novel phenomena emerging from the interplay between lattice geometry, electronic structure, and topology. A prime example is the vanadium-based kagome materials AV3Sb5 (A = K, Rb, and Cs) with superconductivity and unconventional charge-density wave (CDW). More interestingly, the substitution of vanadium by chromium further introduces magnetism and enhances the correlation effect in CsCr3Sb5 which likewise exhibits superconductivity under pressure and competing density-wave state. Here we systematically investigate the electronic structure of CsCr3Sb5 using high-resolution angle-resolved photoemission spectroscopy (APRES) and ab-initio calculations. Overall, the measured electronic structure agrees with the theoretical calculation. Remarkably, Cr 3d orbitals exhibit incoherent electronic states and contribute to incipient flat bands close to the Fermi level. The electronic structure shows a minor change across the magnetic transition at 55 K, suggesting a weak interplay between the local magnetic moment and itinerant electrons. Furthermore, we reveal a drastic enhancement of the electron scattering rate across the magnetic transition, which is relevant to the semiconducting-like transport property of the system at high temperatures. Our results suggest that CsCr3Sb5 is a strongly correlated Hund's metal with incipient flat bands near the Fermi level, which provides an electronic basis for understanding its novel properties in comparison to the non-magnetic and weakly correlated AV3Sb5.