Electronic and superconducting properties of the ${\mathrm{Ti}}_3$P-type compounds ${\mathrm{Nb}}_3$As and ${\mathrm{Nb}}_3$Si

Superconductivity has been observed below temperatures of about 0.3 K in the tetragonal ${\mathrm{Ti}}_3$P-type compounds ${\mathrm{Nb}}_3$Si and ${\mathrm{Nb}}_3$As. Measurements of the electrical resistivity, heat capacity, superconducting transition temperature, and the critical magnetic field curve are reported. From these measurements, values of the electronic specific-heart coefficient $\gamma$, the Debye temperature $\Theta$, the electron-phonon coupling constant $\lambda$, and the Ginzburg-Landau parameter $\kappa$, are deduced. Both compounds have low $\gamma$ values (${\gamma }_{{\mathrm{Nb}}_3\mathrm{Si}}\approx 2.15$ mJ/${\mathrm{K}}^2$g-atom and ${\gamma }_{{\mathrm{Nb}}_3\mathrm{As}}\approx 0.9$ mJ/${\mathrm{K}}^2$g-atom) which probably accounts for the low transition temperatures. A comparison of their electronic and superconducting properties with those of $A_{3}B$ compounds of the $A15$ type suggests that the electron-phonon interaction is quite large in these ${\mathrm{Ti}}_3$P-type materials.