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

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.

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• Flat bands in condensed-matter systems -- perspective for magnetism and superconductivity
• Breathing-Driven Metal-Insulator Transition in Correlated Kagome Systems
• Superconductivity and Electron Correlations in Kagome Metal LuOs3B2
• Identifying Instabilities with Quantum Geometry in Flat Band Systems
• Emergent dynamical Kondo coherence and competing magnetic order in a correlated kagome flat-band metal CsCr6Sb6
• Precompression engineering of metal-insulator transition and magnetism in designed breathing kagome systems
• Theory of unconventional magnetism in a Cu-based kagome metal
• Complex Temperature-dependent Thermal Conductivity in a Sawtooth Chain Magnet Fe${}_2$SiSe${}_4$
• Enhanced Andreev Reflection in Flat-Band Systems: Wave Packet Dynamics, DC Transport and the Josephson Effect