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The interrelationship between flat bands and correlated phenomena such as unconventional superconductivity stands as an intriguing subject in condensed matter physics. Here, by first-principles calculations and random phase approximation analyses, we investigate the electronic structure, superconducting instability, as well as roles of the incipient flat bands in kagome superconductor CsCr₃Sb₅. Our calculations reveal strong antiferromagnetic spin fluctuations in CsCr₃Sb₅, which mediates two sets of spin-singlet superconducting orders with s_- and (dₗₘ, dₗℂ-ₘℂ) -wave symmetries. Under the dominance of local Coulomb interactions, the unoccupied incipient flat bands are shown to be crucial for the momentum dependence of spin fluctuations and thus the superconductivity. Our further analyses unveil a sublattice-momentum-coupling-driven mechanism for this momentum-dependent enhancement of the fluctuations, which provides us a new perspective for future studies of geometrically frustrated systems.
Wu et al. (Sat,) studied this question.