Berlin 2024 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 50: Superconductivity: Theory II
TT 50.8: Vortrag
Mittwoch, 20. März 2024, 17:00–17:15, H 3005
Bypassing the BCS-to-BEC crossover in strongly correlated superconductors: resilient coherence from multiorbital physics — •Niklas Witt1,2, Yusuke Nomura3, Sergey Brener1, Ryotaro Arita4,5, Alexander I. Lichtenstein1,2, and Tim Wehling1,2 — 1University of Hamburg, Germany — 2The Hamburg Centre for Ultrafast Imaging, Germany — 3Keio University, Japan — 4University of Tokyo, Japan — 5RIKEN CEMS, Japan
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 commonly known as the BCS-to-BEC crossover. In this study [1], we report on the circumvention of the BCS-BEC crossover present in a multi-orbital model of alkali-doped fullerides (A3C60). Our findings reveal a localized superconducting regime characterized by a robustly short coherence length and a domeless rise in critical temperature with increasing pairing interaction. We identify strong correlations and multi-orbital effects as the underlying cause of this behavior. These insights are derived from the development of a theoretical framework to calculate the fundamental intrinsic length scales of superconductors, namely the coherence length (ξ0) and the London penetration depth (λL). Importantly, our approach allows for the determination of these scales in microscopic theories and from first principles, even in the presence of strong electron correlations.
[1] N. Witt et al., arXiv:2310.09063 (2023)
Keywords: alkali-doped fullerides; BCS-BEC crossover; unconventional superconductivity; coherence length; Dynamical Mean-Field Theory (DMFT)