Density-Induced Breaking of Pairs in the Attractive Hubbard Model

TL;DR

This paper investigates how increasing particle density in the two-dimensional attractive Hubbard model leads to the breaking of pairs, revealing a critical density where pairing vanishes and pseudogap phenomena occur.

Contribution

It introduces a self-consistent T-matrix approach applied directly in real-frequency domain to study density effects on pairing in the attractive Hubbard model.

Findings

Pair binding energy decreases with density and vanishes at critical density

Pseudogap appears at low densities and temperatures

Critical density for pair breaking is approximately 0.19

Abstract

A conserving T-matrix approximation is applied to the two-dimensional attractive Hubbard model in the low-density regime. A set of self-consistent equations is solved in the real-frequency domain to avoid the analytic continuation procedure. By tuning the chemical potential the particle density was varied in the limits 0.01 < n < 0.18. For the value of the attractive potential U=8t the binding energy of pairs monotonically decreases with increasing n, from its zero-density limit 2.3t and vanishes at a critical density n=0.19. A pairing-induced pseudogap in the single-particle density of states is found at low densities and temperatures.