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Evidence of Strong-Coupled Superconductivity in CaC6 from Tunneling Spectroscopy

C. Kurter·L. Ozyuzer·Daniel Mazur·J. F. Zasadzinski·D. Rosenmann·H. Claus·D. G. Hinks·K. E. Gray
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Abstract

Point-contact tunneling on CaC$_6$ crystals reproducibly reveals superconducting gaps, $Δ$, 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$Δ$/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.

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C. Kurter, L. Ozyuzer, Daniel Mazur, J. F. Zasadzinski, D. Rosenmann, H. Claus, D. G. Hinks, K. E. Gray. 2007-04-26. Evidence of Strong-Coupled Superconductivity in CaC6 from Tunneling Spectroscopy. https://doi.org/10.1103/physrevb.76.220502

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