Superconductivity in the ternary intermetallics of La3Ni4X4 (X = Si and Ge)

Superconductivity in the ternary intermetallics of La3Ni4X4 (X = Si and Ge) with the combination of AlB2 and BaAl4 layers is reported. Both compounds are type II superconductors with critical temperatures (T-c) of 1.0 and 0.70 K for X = Si and Ge, respectively. The lower and the upper critical fields (H-c1(0) and H-c2(0)) for X = Si are 107 Oe and 16.5 kOe, whereas those for X = Ge are 68 Oe and 2.6 kOe, respectively. The gradient -dH(c2)/dT of La3Ni4Si4 is extraordinarily higher than those of the other three analogues of La3Ni4Ge4 and La3Pd4X4. The magnetic penetration depth (lambda(0)) of 202 nm and Ginzburg-Landau coherence length (xi(0)) of 14 nm are derived for X = Si, while they are 206 and 36 nm for X = Ge.