Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary

Potocnik, A., Krajnc, A., Jeglic, P., Takabayashi, Y., Ganin, A. , Prassides, K., Rosseninsky, M. J. and Arcon, D. (2014) Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary. Scientific Reports, 4, 4265. (doi:10.1038/srep04265) (PMID:24584087) (PMCID:PMC3939459)

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Abstract

The alkali fullerides, A3C60 (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs3C60 polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/kBTc = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/kBTc decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Ganin, Dr Alexey
Authors: Potocnik, A., Krajnc, A., Jeglic, P., Takabayashi, Y., Ganin, A., Prassides, K., Rosseninsky, M. J., and Arcon, D.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Scientific Reports
Publisher:Nature Publishing Group
ISSN:2045-2322
ISSN (Online):2045-2322
Copyright Holders:Copyright © 2014 Macmillan Publishers Limited
First Published:First published in Scientific Reports 4:4265
Publisher Policy:Reproduced under a Creative Commons License

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