Single Crystal Growth and Superconductivity in La₇Ni₃ without Inversion Symmetry in the Crystal Structure

We succeeded in growing single crystals of La₇Ni₃ with the non-centrosymmetric hexagonal structure by the Bridgman method, and measured the electrical resistivity and specific heat under magnetic fields. The superconducting transition temperature T_sc is 2.4 K. The electronic specific heat coefficient γ is 44 mJ/(K²-f.u.-mol). Correspondingly, the upper critical field H_c2(0) in superconductivity is large, H_c2 = 27 kOe. The electronic specific heat shows the jump at T_sc = 2.4 K, indicating the bulk superconductivity with ΔC_e/γT_c = 1.2, which is close to the weak coupling BCS value of 1.43. Although the temperature dependence of specific heat and some parameters of superconductivity are well explained by the conventional BCS model, the temperature dependence of H_c2 is not consistent with the simple BCS model.