BCS - BEC crossover at T=0: A Dynamical Mean Field Theory Approach

TL;DR

This paper investigates the BCS-BEC crossover at zero temperature using dynamical mean field theory, revealing significant quantum fluctuation effects that alter the superconducting properties beyond traditional mean field predictions.

Contribution

It applies DMFT with perturbation theory to study quantum fluctuations in the BCS-BEC crossover, highlighting their impact on spectral functions and order parameters.

Findings

Quantum fluctuations reduce the superconducting gap and order parameter.

Spectral functions show incoherent weight beyond the quasiparticle peaks.

Significant deviations from Hartree-Fock-Bogoliubov results in intermediate coupling.

Abstract

We study the T=0 crossover from the BCS superconductivity to Bose-Einstein condensation in the attractive Hubbard Model within dynamical mean field theory(DMFT) in order to examine the validity of Hartree-Fock-Bogoliubov (HFB) mean field theory, usually used to describe this crossover, and to explore physics beyond it. Quantum fluctuations are incorporated using iterated perturbation theory as the DMFT impurity solver. We find that these fluctuations lead to large quantitative effects in the intermediate coupling regime leading to a reduction of both the superconducting order parameter and the energy gap relative to the HFB results. A qualitative change is found in the single-electron spectral function, which now shows incoherent spectral weight for energies larger than three times the gap, in addition to the usual Bogoliubov quasiparticle peaks.