Attractive Hubbard model and single-particle pseudogap due to classical pairing fluctuations in two dimensions

TL;DR

This paper demonstrates that in the two-dimensional attractive Hubbard model, classical pairing fluctuations induce a pseudogap in the single-particle spectral weight, especially in strongly anisotropic quasi-2D materials, differing from preformed pairs.

Contribution

It introduces the concept that classical pairing fluctuations replace the mean-field transition, leading to a pseudogap distinct from preformed pairs, in the 2D attractive Hubbard model.

Findings

Pseudogap arises from classical fluctuations in 2D Hubbard model.

Pseudogap occurs only in strongly anisotropic quasi-2D materials.

Differences between superconducting and magnetic pseudogaps are discussed.

Abstract

It is shown that in the two-dimensional attractive Hubbard model, the mean-field phase transition is replaced by a renormalized classical regime of fluctuations where a pseudogap opens up in the single-particle spectral weight. It is argued that this pseudogap and precursors of the ordered state quasiparticles can occur only in strongly anisotropic quasi two-dimensional materials. This precursor phenomenon differs from preformed local pairs. Furthermore, while critical antiferromagnetic fluctuations would also lead to a pseudogap in the repulsive model, there are some important differences between the superconducting and magnetic pseudogap.