Large energy gaps inCaC6from tunneling spectroscopy: Possible evidence of strong-coupling superconductivity

Cihan Kurter, Lutfi Ozyuzer, Daniel Mazur, John F. Zasadzinski, Daniel Rosenmann, Helmut Claus, Dave G. Hinks, Kenneth E. Gray
2007 Physical Review B  
Point-contact tunneling on CaC_6 crystals reproducibly reveals superconducting gaps, Δ, of 2.3±0.2 meV which are ∼ 40 than earlier reports. That puts CaC_6 into the class of very strong-coupled superconductors since 2Δ/kT_c∼ 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.
doi:10.1103/physrevb.76.220502 fatcat:uhntoyoejjbonirzhr7eufqfqm