With powder-x-ray-diffraction methods, the ternary compound LaNiSi has been identified to have a LaPtSi-type crystal structure with four formula units in a unit cell of the space group I$4_1$md with dimensions a=4.181(1) Å, c=14.069(8) Å. The agreement of the transition temperature ${\mathit{T}}_{\mathit{c}}$=1.20∼1.26 K (10∼90 % values) measured by ac-susceptibility and heat-capacity techniques provides clear evidence of bulk superconductivity in LaNiSi. The normal-state specific-heat data can be fit to the expression ${\mathit{C}}_{\mathit{n}}$=γT+β${\mathit{T}}^3$ by a least-squares analysis, where γ=8.89 mJ/mol ${\mathrm{K}}^2$ and β=0.487 mJ/mol ${\mathrm{K}}^4$, resulting in a Debye temperature ${\mathrm{\Theta }}_{\mathit{D}}$=229 K. Below ${\mathit{T}}_{\mathit{c}}$, the specific-heat data have a dominant low-temperature behavior of the form exp[-Δ(0)/${\mathit{k}}_{\mathit{BT}}$], where the order parameter 2Δ(0)=3.5${\mathit{k}}_{\mathit{BT}\mathit{c}}$. In addition, the measured heat-capacity jump ΔC at the transition point is found to be equal to 1.46γ${\mathit{T}}_{\mathit{c}}$, implying that LaNiSi is a weakly coupled superconductor.

DOI:https://doi.org/10.1103/PhysRevB.50.6523