Incipient antiferromagnetism and low-energy excitations in the half-filled two-dimensional Hubbard model

TL;DR

This study investigates the low-energy excitations and incipient antiferromagnetism in the half-filled 2D Hubbard model, revealing how spin fluctuations influence quasiparticle behavior at different temperatures.

Contribution

It provides a detailed analysis of the evolution of quasiparticles and spin fluctuations in the 2D Hubbard model using the self-consistent fluctuation exchange approximation, highlighting the emergence of pseudogap features.

Findings

Quasiparticles have short lifetimes at moderate temperatures and small U.

Lowering temperature causes quasiparticle extinction due to spin fluctuations.

A simple spin-fluctuation model explains the observed phenomena.

Abstract

We present single-particle and thermodynamic properties of the half-filled single-band Hubbard model in 2D calculated in the self-consistent fluctuation exchange approximation. The low-energy excitations at moderate temperatures and small $U$ are quasiparticles with a short lifetime. As the temperature is lowered, coupling to evolving spin fluctuations leads to the extinction of these quasiparticles, signaled by a weak pseudogap in the density of states and by a positive slope in Re $\Sigma ({\bf k}_F, \varepsilon)$ and a local maximum in $|$Im $\Sigma ({\bf k}_F, \varepsilon)|$ at $\varepsilon = 0$. We explain these results using a simple spin-fluctuation model.