We perform a fluctuation analysis of the pairing interaction in the hole-doped Hubbard model within the dynamical cluster approximation. Our analysis reveals that spin-fluctuation-mediated pairing differs qualitatively in the over- and underdoped regimes. In the underdoped regime, spin fluctuations open a pseudogap. We show that in this regime the spin-fermion coupling mediates a giant attraction between antinodal fermions. This explains why superconductivity survives at underdoping in the Hubbard model and cuprates, despite the lack of coherent fermionic quasiparticles in the pseudogap regime.
@article{arxiv.2410.01705,
title = {Pairing boost from enhanced spin-fermion coupling in the pseudogap regime},
author = {Yang Yu and Sergei Iskakov and Emanuel Gull and Karsten Held and Friedrich Krien},
journal= {arXiv preprint arXiv:2410.01705},
year = {2025}
}