BCS to Bose Crossover in Anisotropic Superconductors

TL;DR

This paper investigates the BCS to Bose-Einstein condensation crossover in anisotropic superconductors using a Hubbard model, revealing a transition from s-wave to d-wave pairing and discussing pseudogap origins.

Contribution

It introduces a phenomenological model for high-Tc cuprates that captures the BCS-BEC crossover and mixed pairing symmetries, including fluctuation effects.

Findings

Transition from s-wave to d-wave superconductivity with doping.

Existence of a mixed s+id pairing state.

Discussion of pseudogap origin and symmetry.

Abstract

In this work we use functional integral techniques to examine the nearest neighbour attractive Hubbard model on a quasi-2D lattice. It is a simple phenomenological model for the high-Tc cuprates that allows both extended (non-local) s- and d-wave singlet superconductivity as well as mixed symmetry states. The Hartree-Gor'kov mean field theory of the model has a finite temperature phase diagram which shows a transition from pure s-wave to pure d-wave superconductivity, via a mixed symmetry s+id state, as a function of doping. Including Gaussian fluctuations we examine the crossover from weak-coupling BCS superconductivity to the strong-coupling Bose-Einstein condensation of composite s- or d-wave bosons and comment on the origin and symmetry of the pseudogap.