Role of spin-orbit coupling in the physical properties of LaX3 (X=In, P, Bi) superconductors

Abstract

We report a comprehensive and complementary study on structural, elastic, mechanical, electronic, phonon, and electron-phonon interaction properties of LaX3 (X = In, Pb, and Bi) using first-principles density functional calculations within the local density approximation with andwithout the spin-orbit coupling (SOC). The calculated lattice parameters for these intermetallic compounds with andwithoutSOCare found to differ by less than2% from their experimental values. The effect of SOC on the elastic, mechanical, electronic, phonon, and electron-phonon interaction properties is more profound for LaPb3 and LaBi3 containing heavier X elements rather than LaIn3 containing lighter X element. The inclusion of SOC considerably removes the degeneracies of some bands near the Fermi level and makes some phonon branches in LaPb3 and LaBi3 softer and increases the strength of dominant peaks in their Eliashberg spectral functions. Thus the SOC related enhancement of their electron-phonon coupling parameter values can be related to both a softening of their phonon dispersion curves and an increase in their electron-phonon coupling matrix elements. The superconducting transition temperature with SOC is computed to be 0.69 K for LaIn3, 4.23 K for LaPb3, and 6.87 K for LaBi3, which agree very well with the respective measured values of 0.70, 4.18, and 7.30 K.