Flat-Band Enhanced Antiferromagnetic Fluctuations and Superconductivity in Pressurized CsCr$_3$Sb$_5$

TL;DR

This study uses first-principles calculations and RPA analyses to reveal that pressurized CsCr$_3$Sb$_5$ exhibits strong antiferromagnetic fluctuations and potential superconductivity near flat bands, driven by a novel sublattice-momentum mechanism.

Contribution

It introduces a new sublattice-momentum-coupling mechanism explaining antiferromagnetic fluctuations in kagome systems near flat bands, expanding understanding of magnetic and superconducting behaviors.

Findings

Strong antiferromagnetic spin fluctuations near flat bands.

Possible $s_{}$-wave and $d$-wave superconductivity.

Mechanism applicable to other kagome systems.

Abstract

The spin dynamics and electronic orders of the kagome system at different filling levels stand as an intriguing subject in condensed matter physics. By first-principles calculations and random phase approximation analyses, we investigate the spin fluctuations and superconducting instabilities in kagome phase of CsCr$_3$Sb$_5$ under high pressure. At the filling level slightly below the kagome flat bands, our calculations reveal strong antiferromagnetic spin fluctuations in CsCr$_3$Sb$_5$, together with a leading $s_{\pm}$-wave and a competing ($d_{xy}$, $d_{x^2-y^2}$)-wave superconducting order. Unlike the general intuition that the flat bands are closely related to the ferromagnetic correlations, here we propose a sublattice-momentum-coupling-driven mechanism for the antiferromagnetic fluctuations enhanced from the unoccupied flat bands. The mechanism is generally applicable to kagome systems where the Fermi level intersects near the flat bands, offering a new perspective for future studies of geometrically frustrated systems.