English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We use the variational cluster approximation to study the superconductingground state in the two-dimensional attractive Hubbard model, puttingparticular emphasis on the significance of quantum fluctuations of the system.We first show that the order parameter is suppressed in comparison with thatobtained using the mean-field theory owing to the effects of spatialfluctuations in two-dimensional systems. We then show that the calculatedBogoliubov quasiparticle spectra and condensation amplitude clearly exhibit thecharacter of Cooper pairs in momentum space and that the pair coherence length$\xi$ evaluated from the condensation amplitude demonstrates a smooth crossoverin real space from a weakly paired BCS state ($\xi\gg a$) to a BEC state oftightly bound pairs ($\xi\ll a$), where $a$ is the lattice constant. Thecalculated kinetic and potential energies in the superconducting and normalground states indicate that the superconducting state in the weak-couplingregion is driven by the gain in potential energy, while that in thestrongcoupling region is driven by the gain in kinetic energy.

BCS-BEC Crossover in the Two-Dimensional Attractive Hubbard Model: Variational Cluster Approach