Fermi level tuning and double-dome superconductivity in the kagome metals CsV$_3$Sb$_{5-x}$Sn$_x$

TL;DR

This study explores how chemical doping in kagome metals CsV$_3$Sb$_{5}$ tunes the Fermi level, leading to double-dome superconductivity and suppression of charge density wave order, revealing unconventional coupling between these states.

Contribution

It demonstrates how hole-doping via Sn substitution modulates the electronic structure and superconducting phases, unveiling a double-dome superconducting behavior in CsV$_3$Sb$_{5-x}$Sn$_x$.

Findings

Superconducting transition temperature exhibits two peaks at 3.6 K and 4.1 K.

Charge density wave order is rapidly suppressed with hole doping.

Complete suppression of superconductivity correlates with an electron-like band crossing above E_F.

Abstract

The recently reported \textit{A}V$_3$Sb$_5$ (\textit{A} = K, Rb, Cs) family of kagome metals are candidates for unconventional superconductivity and chiral charge density wave (CDW) order; both potentially arise from nested saddle points in their band structures close to the Fermi energy. Here we use chemical substitution to introduce holes into CsV$_3$Sb$_{5}$ and unveil an unconventionalcoupling of the CDW and superconducting states. Specifically, we generate a phase diagram for CsV$_3$Sb$_{5-x}$Sn$_{x}$ that illustrates the impact of hole-doping the system and lifting the nearest vHs toward and above $E_F$. Superconductivity exhibits a non-monotonic evolution with the introduction of holes, resulting in two "domes" peaked at 3.6\,K and 4.1\,K and the rapid suppression of three-dimensional CDW order. The evolution of CDW and superconducting order is compared with the evolution of the electronic band structure of CsV$_3$Sb$_{5-x}$Sn$_x$, where the complete suppression of superconductivity seemingly coincides with an electron-like band comprised of Sb $p_z$ orbitals pushed above E$_F$.