A unique van Hove singularity in kagome superconductor CsV$_{3-x}$Ta$_x$Sb$_5$ with enhanced superconductivity

TL;DR

This paper reports the discovery of a van Hove singularity at the Fermi level in a kagome superconductor CsV$_{3-x}$Ta$_x$Sb$_5$, which correlates with record-high superconducting transition temperature and provides insights into enhanced superconductivity mechanisms.

Contribution

It demonstrates the presence of a perfectly aligned van Hove singularity at the Fermi level in CsV$_{3-x}$Ta$_x$Sb$_5$, linking it to increased superconductivity, a novel finding in kagome superconductors.

Findings

VHS aligned with Fermi level in CsV$_{3-x}$Ta$_x$Sb$_5$

Record-high superconducting transition temperature achieved

Spectroscopic evidence of a distinct superconducting state

Abstract

Van Hove singularity (VHS) has been considered as a driving source for unconventional superconductivity. A VHS in two-dimensional (2D) materials consists of a saddle point connecting electron-like and hole-like bands. In a rare case, when a VHS appears at Fermi level, both electron-like and hole-like conduction can coexist, giving rise to an enhanced density of states as well as an attractive component of Coulomb interaction for unconventional electronic pairing. However, this van Hove scenario is often destroyed by an incorrect chemical potential or competing instabilities. Here, by using angle-resolved photoemission measurements, we report the observation of a VHS perfectly aligned with the Fermi level in a kagome superconductor CsV$_{3-x}$Ta$_x$Sb$_5$ (x~0.4), in which a record-high superconducting transition temperature is achieved among all the current variants of AV$_3$Sb$_5$ (A=Cs, Rb, K) at ambient pressure. Doping dependent measurements reveal the important role of van Hove scenario in boosting superconductivity, and spectroscopic-imaging scanning tunneling microscopy measurements indicate a distinct superconducting state in this system.