Rich Nature of Van Hove Singularities in Kagome Superconductor CsV$_3$Sb$_5$

TL;DR

This study combines experimental and theoretical methods to reveal the complex nature of van Hove singularities in CsV$_3$Sb$_5$, highlighting their sublattice properties and the discovery of higher-order VHSs, which are key to understanding its correlated phenomena.

Contribution

It provides the first direct experimental identification of sublattice-specific van Hove singularities and higher-order VHSs in CsV$_3$Sb$_5$ using ARPES and DFT.

Findings

Identification of four VHSs near the M point, three close to the Fermi level.

Discovery of a higher-order VHS with flat dispersion along MK.

Observation of sublattice interference effects in Dirac cone intensity modulation.

Abstract

The recently discovered layered kagome metals AV$_3$Sb$_5$ (A=K, Rb, Cs) exhibit diverse correlated phenomena, which are intertwined with a topological electronic structure with multiple van Hove singularities (VHSs) in the vicinity of the Fermi level. As the VHSs with their large density of states enhance correlation effects, it is of crucial importance to determine their nature and properties. Here, we combine polarization-dependent angle-resolved photoemission spectroscopy with density functional theory to directly reveal the sublattice properties of 3d-orbital VHSs in CsV$_3$Sb$_5$. Four VHSs are identified around the M point and three of them are close to the Fermi level, with two having sublattice-pure and one sublattice-mixed nature. Remarkably, the VHS just below the Fermi level displays an extremely flat dispersion along MK, establishing the experimental discovery of higher-order VHS. The characteristic intensity modulation of Dirac cones around K further demonstrates the sublattice interference embedded in the electronic structure. The crucial insights into the electronic structure, revealed by our work, provide a solid starting point for the understanding of the intriguing correlation phenomena in the kagome metals AV$_3$Sb$_5$.