Superconductivity in an extended Hubbard model with attractive interaction

TL;DR

This paper investigates a two-dimensional Hubbard model with non-local attractive interactions to understand d-wave superconductivity, revealing complex gap behavior, quasiparticle structures, and Fermi surface topology, with connections to experimental findings.

Contribution

It introduces a two-pole approximation to analyze a Hubbard model with attractive interactions, providing new insights into the superconducting gap and electronic structure.

Findings

Complex temperature dependence of the superconducting gap

Detailed quasiparticle band structures analyzed

Fermi surface topology changes with temperature

Abstract

In this work, a two-dimensional one-band Hubbard model is investigated within a two-pole approximation. The model presents a non-local attractive potential $U (U<0)$ that allows the study of d-wave superconductivity and also includes hopping up to second-nearest-neighbors. The two-pole scheme has been proposed to improve the Hubbard-I approximation. The analytical results show a more complex form for the gap $\Delta(T)$, when compared to the one obtained in the latter approximation. Indeed, new anomalous correlation functions associated with the superconductivity are involved in the calculation of $\Delta(T)$. Numerical results in a range of temperatures are presented. Moreover, the structure of the quasiparticle bands and the topology of the Fermi surface are studied in detail in the normal state. Connections with some experimental results are also included.