Evidence for s-wave pairing from measurement on lower critical field in $MgCN{i}_3$

Abstract

Magnetization measurements in the low field region have been carefully performed on a well-shaped cylindrical and an ellipsoidal sample of superconductor $MgCN{i}_3$. Data from both samples show almost the same results. The lower critical field $H_{c1}$ and the London penetration depth $\hat{I}»$ are thus derived. It is found that the result of normalized superfluid density $\hat{I}{»}^2(0)/\hat{I}{»}^2(T)$ of $MgCN{i}_3$ can be well described by BCS prediction with the expectation for an isotropic s-wave superconductivity.

To appear in Phys. Rev. B