Evidence of Strong-Coupled Superconductivity in CaC6 from Tunneling Spectroscopy

Abstract

Point-contact tunneling on CaC${}_6$ crystals reproducibly reveals superconducting gaps, $\Delta$, of 2.3$\pm$0.2 meV which are $\sim$~40% larger than earlier reports. That puts CaC${}_6$ into the class of very strong-coupled superconductors since 2$\Delta$/kT${}_c\sim$~4.6. Thus soft Ca phonons will be primarily involved in the superconductivity, a conclusion that explains the large Ca isotope effect found recently for CaC${}_6$. Consistency among superconductor-insulator-normal metal (SIN), SIS and Andreev reflection (SN) junctions reinforces the intrinsic nature of this result.

2nd version, 4 pages, 4 figures, re-submitted to Physical Review Letters

References in corpus (3)

• Scanning Tunneling Spectroscopy on the novel superconductor CaC6
• Specific Heat of the Ca-Intercalated Graphite Superconductor CaC${}_6$
• Unresolved problems in superconductivity of CaC6

Cited by in corpus (3)

• Evidence for gap anisotropy in CaC6 from directional point-contact spectroscopy
• Raman scattering from the CaC6 superconductor in the presence of disorder
• Far-infrared signature of the superconducting gap in intercalated graphite CaC6