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

Abstract

Specific heat has been measured down to 600 mK and up to 8 Tesla by the highly sensitive AC microcalorimetry on the 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 2D/kTc ~ 4. This scenario is supported by the direct gap measurements via the point-contact spectroscopy. Moreover, the spectroscopy measurements show a decrease in the critical temperature at the sample surface accounting for the observed differences of the superfluid density deduced from the measurements by different techniques.

References in corpus (5)

• Thermodynamic phase diagram of Fe(Se${}_{0.5}$Te${}_{0.5}$) single crystals up to 28 Tesla
• Specific-heat measurements of superconducting NbS2 single crystal in an external magnetic field: Study on the energy gap structure
• Evidence for strong electron-phonon coupling in MgCNi_3
• S-wave superconductivity probed by measuring magnetic penetration depth and lower critical field of MgCNi${}_3$ single crystals
• The effect of Fe and Ru substitution for Ni on the thermopower in MgCNi_3

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• Vacancies, disorder-induced smearing of the electronic structure, and its implications for the superconductivity of anti-perovskite MgC${}_{0.93}$Ni${}_{2.85}$
• Superconductivity in the vicinity of ferromagnetism in oxygen free perovskite MgCNi3: An experimental and DFT (Density Functional Theory) study