La4TX (T = Ru, Rh, Ir; X = Al, In): A family of noncentrosymmetric superconductors with tunable antisymmetric spin-orbit coupling

We report the discovery of superconductivity in a series of noncentrosymmetric compounds La4TX (T = Ru, Rh, Ir; X = Al, In), which have a cubic crystal structure with the space group F (4) over bar 3m. La4RuAl, La4RhAl, La4IrAl, La4RuIn and La4IrIn exhibit bulk superconducting transitions with critical temperatures (T-c) of 0.61-3.35 K, while La4RhIn was not successfully synthesized. The specific heats of La4RuAl and La4RhAl are best accounted for by an s-wave model with a fully open superconducting gap, while a nodal gap cannot be excluded for La4IrAl, which has stronger antisymmetric spin-orbit coupling (ASOC). In all cases, the upper critical fields are well described by the Werthamer-Helfand-Hohenberg model, and the values are well below the Pauli limit, indicating that orbital limiting is the dominant pair-breaking mechanism. Density functional theory (DFT) calculations reveal that the degree of band splitting by the ASOC shows considerable variation between the different compounds. This indicates that the strength of the ASOC is highly tunable across this series of superconductors, suggesting that they are good candidates for examining the relationship between ASOC and superconducting properties in noncentrosymmetric superconductors.

Automated summary

We report the discovery of superconductivity in a series of noncentrosymmetric compounds La4TX, with La4RuAl and La4RhAl best described by an s-wave model and La4IrAl possibly having a nodal gap. The upper critical fields in all compounds are well described by the Werthamer-Helfand-Hohenberg model, indicating orbital limiting as the dominant pair-breaking mechanism. Density functional theory calculations show that the strength of antisymmetric spin-orbit coupling varies across this series of superconductors, making them good candidates for studying the relationship between ASOC and superconducting properties in noncentrosymmetric superconductors.