Superconductivity in the ternary intermetallics of La₃Ni ₄X₄ (X = Si and Ge)

Superconductivity in the ternary intermetallics of La₃Ni ₄X₄ (X = Si and Ge) with the combination of AlB ₂ and BaAl₄ layers is reported. Both compounds are type II superconductors with critical temperatures (T_c) of 1.0 and 0.70K for X = Si and Ge, respectively. The lower and the upper critical fields (H _c1(0) and H_c2(0)) for X = Si are 107Oe and 16.5kOe, whereas those for X = Ge are 68Oe and 2.6kOe, respectively. The gradient -dH_c2/dT of La₃Ni₄Si₄ is extraordinarily higher than those of the other three analogues of La ₃Ni₄Ge₄ and La₃Pd₄X ₄. The magnetic penetration depth (λ(0)) of 202nm and Ginzburg-Landau coherence length (ξ(0)) of 14nm are derived for X = Si, while they are 206 and 36nm for X = Ge.