Three-dimensional charge density wave and robust zero-bias conductance peak inside the superconducting vortex core of a kagome superconductor CsV$_3$Sb$_5$

TL;DR

This study reveals a three-dimensional charge density wave and a stable zero-bias conductance peak inside vortices in the kagome superconductor CsV$_3$Sb$_5$, indicating potential Majorana bound states and exotic quasiparticle excitations.

Contribution

It provides the first direct STM evidence of 3D charge density wave order and zero-bias peaks in CsV$_3$Sb$_5$, linking topology, charge order, and superconductivity in a kagome metal.

Findings

Charge modulation exhibits a {\

Zero-bias conductance peak remains stable inside vortex cores.

Charge density wave shows a {\

Abstract

The transition-metal-based kagome metals provide a versatile platform for correlated topological phases hosting various electronic instabilities. While superconductivity is rare in layered kagome compounds, its interplay with nontrivial topology could offer an engaging space to realize exotic excitations of quasiparticles. Here, we use scanning tunneling microscopy (STM) to study a newly discovered Z$_2$ topological kagome metal CsV$_3$Sb$_5$ with a superconducting ground state. We observe charge modulation associated with the opening of an energy gap near the Fermi level. When across single-unit-cell surface step edges, the intensity of this charge modulation exhibits a {\pi}-phase shift, suggesting a three-dimensional 2$\times$2$\times$2 charge density wave ordering. Interestingly, a robust zero-bias conductance peak is observed inside the superconducting vortex core on the Cs 2$\times$2 surfaces that does not split in a large distance when moving away from the vortex center, resembling the Majorana bound states arising from the superconducting Dirac surface states in Bi$_2$Te$_3$/NbSe$_2$ heterostructures. Our findings establish CsV$_3$Sb$_5$ as a promising candidate for realizing exotic excitations at the confluence of nontrivial lattice geometry, topology and multiple electronic orders.