Superconducting energy gap in MgCNi3 single crystals: Point-contact spectroscopy and specific-heat measurements

Z. Pribulova (1) , J. Kacmarcik (1) , C. Marcenat (2) , P. Szabo (1) , Thierry Klein (3) , A. Demuer (4) , Pierre Rodiere (3) , D. J. Jang (5) , H. S. Lee (5) , H. G. Lee (6) , S.I. Lee (6) , P. Samuely (1)

1 CLTP IEP - Centre of Low Temperature Physics
2 SPSMS - UMR 9001 - Service de Physique Statistique, Magnétisme et Supraconductivité
3 NEEL - MagSup - Magnétisme et Supraconductivité
4 LNCMI-G - Laboratoire national des champs magnétiques intenses - Grenoble
5 NVCRICS
6 Department of Physics, National Creative Research Initiative Center for Superconductivity

Specific heat has been measured down to 600 mK and up to 8 T by highly sensitive ac microcalorimetry on MgCNi3 single crystals with Tc ≈ 7 K. Exponential decay of the electronic specific heat at low temperatures proved that a superconducting energy gap is fully open on the whole Fermi surface, in agreement with our previous magnetic penetration depth measurements on the same crystals. The specific-heat data analysis shows consistently the strong-coupling strength 2 /kBTc ≈ 4. This scenario is supported by the direct measurements of the gap via the point-contact spectroscopy. Moreover, the spectroscopy measurements show a decrease in the critical temperature at the sample surface, which accounts for the observed differences of the superfluid density deduced from the measurements by different techniques.

Mots clés: supraconductivité

Domaines: Supraconductivité [cond-mat.supr-con]

Z. Pribulova, J. Kacmarcik, C. Marcenat, P. Szabo, Thierry Klein, et al.. Superconducting energy gap in MgCNi3 single crystals: Point-contact spectroscopy and specific-heat measurements. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2011, 83, pp.104511. ⟨10.1103/PhysRevB.83.104511⟩. ⟨hal-00957180⟩