Antiferromagnetic Dimers in the Parent Phase of a Correlated Kagome Superconductor

TL;DR

This paper investigates the crystal structure and magnetic interactions of CsCr3Sb5, revealing antiferromagnetic Cr dimers and suggesting their role in electron pairing for superconductivity.

Contribution

It provides the first structural solution of the 4x1 CDW state in CsCr3Sb5 and highlights the significance of antiferromagnetic dimers in its correlated physics.

Findings

CsCr3Sb5 has a 4x1 CDW with Cr dimers and chains.

Antiferromagnetic exchange dominates within Cr dimers.

The CDW transition is strongly first-order without soft phonons.

Abstract

Kagome metals are prone to charge-density wave (CDW), magnetic, and superconducting phases, with their flat electronic band conducive for correlated physics. In contrast to the weakly correlated $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) kagome metals with a $2\times2$ CDW, CsCr$_3$Sb$_5$ is a correlated metal with a flat band close to the Fermi level, and exhibits a $4\times1$ CDW intertwined with magnetic order. Under pressure, the intertwined orders are suppressed and give way to a dome of superconductivity that emerges from a non-Fermi liquid normal state. Here, we solve the crystal structure of the $4\times 1$ CDW state in CsCr$_3$Sb$_5$, and show it consists of Cr dimers separated by Cr chains. First-principles calculations show the dominant exchange interaction is antiferromagnetic within the dimers, while the intra-chain and dimer-chain couplings are much weaker. The CDW transition of CsCr$_3$Sb$_5$ is found to be more strongly first-order than those in $A$V$_3$Sb$_5$, without significant soft phonons or diffuse scattering above the CDW transition temperature. These findings suggest that fluctuating antiferromagnetic dimers may play a major role in the electron pairing of superconducting CsCr$_3$Sb$_5$.