Past colloquia and seminars


Bypassing the BCS-BEC crossover in strongly correlated superconductors: resilient coherence from multiorbital physics

General public Seminar

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-BEC crossover. In this study [1], we report on an enhancement of superconductivity beyond the limits of the conventional 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 multiorbital effects as the underlying cause of this behavior. 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). Importantly, our approach allows for the determination of these scales in microscopic theories and from first principles, even in presence of strong electron correlations.

[1] N. Witt et al., arXiv:2310.09063 (2023)

When? 15.02.2024 11:00
Where? PER 08 2.73
Chemin du Musée 3
1700 Fribourg
speaker Niklas Witt
University of Hamburg
Invité par Prof. Werner
Contact Département de Physique
Prof. Philipp Werner