Charge-Density-Wave-Induced Peak-Dip-Hump Structure and the Multiband Superconductivity in a Kagome Superconductor CsV$_{3}$Sb$_{5}$

TL;DR

This study reveals the complex interplay of charge density waves and multiband superconductivity in the kagome superconductor CsV$_3$Sb$_5$, highlighting the role of flat bands and Dirac dispersions in its electronic structure.

Contribution

It provides high-resolution ARPES evidence of the peak-dip-hump structure and multiband superconductivity, clarifying the relationship between CDW and superconductivity in CsV$_3$Sb$_5$.

Findings

Observation of peak-dip-hump structure near $ar{K}$

Detection of a superconducting gap of ~0.4 meV on multiple bands

Identification of flat band contributions to multiband superconductivity

Abstract

The entanglement of charge density wave (CDW), superconductivity, and topologically nontrivial electronic structure has recently been discovered in the kagome metal $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) family. With high-resolution angle-resolved photoemission spectroscopy, we study the electronic properties of CDW and superconductivity in CsV$_3$Sb$_5$. The spectra around $\bar{K}$ is found to exhibit a peak-dip-hump structure associated with two separate branches of dispersion, demonstrating the isotropic CDW gap opening below $E_{\rm F}$. The peak-dip-hump lineshape is contributed by linearly dispersive Dirac bands in the lower branch and a dispersionless flat band close to $E_{\rm F}$ in the upper branch. The electronic instability via Fermi surface nesting could play a role in determining these CDW-related features. The superconducting gap of $\sim$0.4 meV is observed on both the electron band around $\bar{\Gamma}$ and the flat band around $\bar{K}$, implying the multiband superconductivity. The finite density of states (DOS) at $E_{\rm F}$ in the CDW phase are most likely in favor of the emergence of multiband superconductivity, particularly the enhanced DOS associated with the flat band. Our results not only shed light on the controversial origin of the CDW, but also offer insights into the relationship between CDW and superconductivity.