paper

BCS-BEC Crossover: From High Temperature Superconductors to Ultracold Superfluids

arXiv:cond-mat/0404274 · doi:10.1016/j.physrep.2005.02.005

Abstract

We review the BCS to Bose Einstein condensation (BEC) crossover scenario which is based on the well known crossover generalization of the BCS ground state wavefunction . While this ground state has been summarized extensively in the literature, this Review is devoted to less widely discussed issues: understanding the effects of finite temperature, primarily below , in a manner consistent with . Our emphasis is on the intersection of two important problems: high superconductivity and superfluidity in ultracold fermionic atomic gases. We address the "pseudogap state" in the copper oxide superconductors from the vantage point of a BCS-BEC crossover scenario, although there is no consensus on the applicability of this scheme to high . We argue that it also provides a useful basis for studying atomic gases near the unitary scattering regime; they are most likely in the counterpart pseudogap phase. That is, superconductivity takes place out of a non-Fermi liquid state where preformed, metastable fermion pairs are present at the onset of their Bose condensation. As a microscopic basis for this work, we summarize a variety of -matrix approaches, and assess their theoretical consistency. A close connection with conventional superconducting fluctuation theories is emphasized and exploited.

Final version, in RMP format

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