Coupled electrons and pair fluctuations in two dimensions: a transition to superconductivity in a conserving approximation

TL;DR

This paper presents a self-consistent study of a superconducting phase transition in a two-dimensional Hubbard model, showing agreement with quantum Monte Carlo results and revealing a transition mechanism beyond traditional theories.

Contribution

It introduces a fully self-consistent, conserving approximation to analyze the superconducting transition, providing new insights into the nature of the phase transition in 2D systems.

Findings

Transition temperature agrees with quantum Monte Carlo results

Superfluid density and specific heat behaviors differ from mean-field and Kosterlitz-Thouless predictions

Transition involves coupled collective and electronic degrees of freedom

Abstract

We report on a fully self-consistent determination of a phase transition to a superconducting state in a conserving approximation. The transition temperature calculated for a two-dimensional Hubbard model with an attractive interaction in the fluctuation exchange approximation agrees with quantum Monte Carlo calculations. The temperature dependences of the superfluid density and of the specific heat near the transition temperature indicate that the phase transition in this model of coupled collective degrees of freedom and electronic degrees of freedom is consistent with neither mean-field theory, Gaussian fluctuations about a mean field order parameter, nor unbinding Kosterlitz-Thouless vortices.