Experimental and first-principles studies on superconductivity in noncentrosymmetric La3Se4

We report the synthesis and detailed characterization of superconducting La3Se4, with Tc - 8.5 +/- 0.1 K, using x-ray diffraction, electrical transport, magnetization, and heat capacity measurements. La3Se4 crystallizes in the noncentrosymmetric cubic Th3P4-type structure with space group I4 over bar 3d. Characteristic superconducting parameters such as the lower critical field, upper critical field, thermodynamic critical field, coherence length, penetration depth, and Ginzburg-Landau parameter have been determined. The specific heat jump at Tc, AC/gamma Tc = 2.04 +/- 0.05, exceeds the value for a weakly coupled BCS superconductor, and the electronphonon coupling constant is found to be lambda ep = 0.87 +/- 0.02, suggesting superconductivity in La3Se4 is in the strong-coupling regime. The estimated upper critical field is well below the calculated Pauli limit, and the Maki parameter value (alpha < 1) indicates that the superconducting upper critical field is dominated by orbital pair breaking. From density functional theory based first-principles simulations we observe the number of states at the Fermi energy is dominated mainly by d and f electrons of La. Furthermore, we observe band crossings along the high-symmetry k lines in the vicinity of the Fermi energy. These bands are observed to split due to the removal of spin degeneracy associated with spin-orbit coupling, with the splitting energy EASOC approximate to 65 meV.