# Pairing and non-Fermi liquid behavior in partially flat-band systems

## TL;DR

This study investigates how flat regions in a 2D Hubbard model's band structure influence magnetic fluctuations, pairing symmetries, and non-Fermi liquid behavior, revealing unique correlation effects in partially flat-band systems.

## Contribution

It demonstrates the impact of flat band regions on magnetic crossover, pairing symmetry, and non-Fermi liquid phenomena using FLEX+DMFT in a one-band model.

## Key findings

- Crossover from ferromagnetic to antiferromagnetic fluctuations with band filling
- Transition from triplet to singlet pairing depending on flat region size
- Detection of non-Fermi liquid behavior in spectral and momentum properties

## Abstract

While multiband systems are usually considered for flat-band physics, here we study one-band models that have flat portions in the dispersion to explore correlation effects in the 2D repulsive Hubbard model in an intermediate coupling regime. The FLEX+DMFT~(the dynamical mean-field theory combined with the fluctuation exchange approximation) is used to show that we have a crossover from ferromagnetic to antiferromagnetic spin fluctuations as the band filling is varied, which triggers a crossover from triplet to singlet pairings with a peculiar filling dependence that is dominated by the size of the flat region in the dispersion. A curious manifestation of the flat part appears as larger numbers of nodal lines associated with pairs extended in real space. We further detect non-Fermi liquid behavior in the momentum distribution function, frequency dependence of the self-energy and spectral function. These indicate correlation physics peculiar to flat-band systems.