Tunneling spectroscopy of the superconducting energy gap inRNi2B2C(R=YandLu)

Abstract

Superconducting energy gap in $R{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C} (R=\mathrm{Y}\mathrm{and}\mathrm{Lu})$ has been investigated using a break-junction tunneling technique. The observed differential conductance $\frac{\mathrm{dI}}{\mathrm{dV}}$ is well described by the BCS density of states with a small lifetime broadening parameter. We have found small gap values for the local low-${T}_{c}$ phases in addition to the bulk ${T}_{c}$ of 15.6-16.6 K. The gap value of $2\ensuremath{\Delta}=4.5$ meV with ${T}_{c}=15$ K gives the BCS ratio of $\frac{2\ensuremath{\Delta}}{{k}_{B}{T}_{c}}=3.5$, which is kept constant down to the observed lowest ${T}_{c}$ of 4.6 K. These results give clear evidence for the BCS mechanism of superconductivity for these compounds.