Influence of Carbon Concentration on the Superconductivity in MgCxNi3

Abstract

The influence of carbon concentration on the superconductivity (SC) in MgC${}_x$Ni${}_3$ has been investigated by measuring the low temperature specific heat combined with first principles electronic structure calculation. It is found that the specific heat coefficient ${\gamma }_n=C_{en}/T$ of the superconducting sample ($x\approx 1$) in normal state is twice that of the non-superconducting one ($x\approx 0.85$). The comparison of measured ${\gamma }_n$ and the calculated electronic density of states (DOS) shows that the effective mass renormalization changes remarkably as the carbon concentration changes. The large mass renormalization for the superconducting sample and the low $T_c$(7K) indicate that more than one kind of boson mediated electron-electron interactions exist in MgC${}_x$Ni${}_3$.

4 pages, 4 figures

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• Competition between the BCS superconductivity and ferromagnetic spin fluctuations in MgCNi${}_3$
• S-wave superconductivity probed by measuring magnetic penetration depth and lower critical field of MgCNi${}_3$ single crystals
• Conventional superconductivity and hysteretic Campbell penetration depth in single crystals MgCNi${}_3$
• The role of carbon for superconductivity in MgC${}_x$Ni${}_3$ from specific heat
• Superconducting energy gap in MgCNi3 single crystals: Point-contact spectroscopy and specific-heat measurements
• Role of C in MgC_xNi_3 investigated from first principles
• A first-principles comparison of the electronic properties of MgC_{y}Ni_{3} and ZnC_{y}Ni_{3} alloys
• Rutgers relation for the analysis of superfluid density in superconductors
• The effect of {11}^B substitution on the superconductivity in MgCNi3
• Evidence for s-wave pairing from measurement on lower critical field in $MgCN{i}_3$
• Vacancies, disorder-induced smearing of the electronic structure, and its implications for the superconductivity of anti-perovskite MgC${}_{0.93}$Ni${}_{2.85}$
• The effect of Fe and Ru substitution for Ni on the thermopower in MgCNi_3
• Superconductivity in the vicinity of ferromagnetism in oxygen free perovskite MgCNi3: An experimental and DFT (Density Functional Theory) study