Tuning of superconductivity by Ni substitution into noncentrosymmetric ThCo1−xNixC2

The recently discovered noncentrosymmetric superconductor ${\mathrm{ThCoC}}_{2}$ was observed to show unusual superconducting behavior with a critical temperature of ${T}_{c}=2.65\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Here we investigate the effect of nickel substitution on the superconducting state in $\mathrm{ThC}{\mathrm{o}}_{1\ensuremath{-}x}\mathrm{N}{\mathrm{i}}_{x}{\mathrm{C}}_{2}$. Magnetization, resistivity, and heat capacity measurements demonstrate Ni substitution has a dramatic effect with critical temperature increased up to ${T}_{c}=12.1$ K for $x=0.4$ Ni concentration, which is a rather high transition temperature for a noncentrosymmetric superconductor. In addition, the unusual superconducting characteristics observed in pure ${\mathrm{ThCoC}}_{2}$ appear to be suppressed or tuned with Ni substitution towards a more conventional fully gapped superconductor.