Bypassing the lattice BCS-BEC crossover in strongly correlated superconductors: resilient coherence from multiorbital physics
arxiv(2023)
摘要
Superconductivity emerges from the spatial coherence of a macroscopic
condensate of Cooper pairs. Increasingly strong binding and localization of
electrons into these pairs compromises the condensate's phase stiffness,
thereby limiting critical temperatures - a phenomenon known as the BCS-BEC
crossover in lattice systems. In this study, we report on an enhancement of
superconductivity beyond the limits of the lattice BCS-BEC crossover realized
in a multiorbital model of alkali-doped fullerides (A_3C_60). We show how
strong correlations and multiorbital effects lead into a localized
superconducting regime characterized by a short coherence length but robust
stiffness and a domeless rise in critical temperature with increasing pairing
interaction. These insights are derived from the development of a theoretical
framework to calculate the fundamental length scales of superconductors, namely
the coherence length (ξ_0) and the London penetration depth
(λ_L), in microscopic theories and from first principles,
even in presence of strong electron correlations.
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