Witt Niklas, Nomura Yusuke, Brener Sergey, Arita Ryotaro, Lichtenstein Alexander I, Wehling Tim O
I. Institute of Theoretical Physics, University of Hamburg, Notkestraße 9-11, 22607 Hamburg, Germany.
The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22607 Hamburg, Germany.
NPJ Quantum Mater. 2024;9(1):100. doi: 10.1038/s41535-024-00706-7. Epub 2024 Dec 10.
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 demonstrate enhanced superconductivity in a multiorbital model of alkali-doped fullerides (AC) that goes beyond the limits of the lattice BCS-BEC crossover. We identify that the interplay of strong correlations and multiorbital effects results in a localized superconducting state characterized by a short coherence length but robust stiffness and a domeless rise in critical temperature with increasing pairing interaction. To derive these insights, we introduce a new theoretical framework allowing us to calculate the fundamental length scales of superconductors, namely the coherence length ( ) and the London penetration depth ( ), even in presence of strong electron correlations.
超导性源于库珀对宏观凝聚体的空间相干性。电子越来越强地束缚并定域在这些对中，会损害凝聚体的相位刚度，从而限制临界温度——这种现象在晶格系统中被称为BCS - BEC交叉。在本研究中，我们展示了在碱掺杂富勒烯（AC）的多轨道模型中增强的超导性，该模型超出了晶格BCS - BEC交叉的限制。我们确定，强关联和多轨道效应的相互作用导致了一种局域超导态，其特征是相干长度短但刚度稳健，并且随着配对相互作用的增加，临界温度呈无穹顶上升。为了得出这些见解，我们引入了一个新的理论框架，使我们能够计算超导体的基本长度尺度，即相干长度（ ）和伦敦穿透深度（ ），即使在存在强电子关联的情况下也是如此。
