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

Potocnik, Anton, Krajnc, Andraz, Jeglic, Peter, Takabayashi, Yasuhiro, Ganin, Alexey Y, Prassides, Kosmas, Rosseinsky, Matthew J ORCID: 0000-0002-1910-2483 and Arcon, Denis (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 (1). 4265-. ISSN 2045-2322, 2045-2322

Text Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary.pdf - Published version Download (558kB)

Abstract

The alkali fullerides, A<inf>3</inf> C<inf>60</inf> (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.) Cs<inf>3</inf> C<inf>60</inf> 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, 2Δ<inf>0</inf>/k<inf>B</inf> T<inf>c</inf> = 5.3(2) [Δ<inf>0</inf> = Δ(0 K)]. 2Δ<inf>0</inf>/k <inf>B</inf>T<inf>c</inf> 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 T<inf>c</inf> 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:	Article
Uncontrolled Keywords:	51 Physical Sciences, 5104 Condensed Matter Physics
Depositing User:	Symplectic Admin
Date Deposited:	01 Aug 2016 16:01
Last Modified:	24 Jun 2026 12:52
DOI:	10.1038/srep04265
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3002643
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