The influence of spin orbit interaction on phonons and superconductivity in the noncentrosymmetric superconductors LaPt 3 Si and LaPtSi 3

Abstract

We have performed ab initio study of structural, electronic, vibrational and electronphonon interaction properties of LaPt 3 Si and LaPtSi 3 by employing the density functional theory, a linear-response formalism, and the plane-wave pseudopotential method. The electronic structure, phonon dispersion relations and the Eliashberg spectral function for these materials have been examined with and without the inclusion of spin-orbit interaction (SOI). Our electron-phonon interaction results reveal that the influence of spin-orbit interaction on phonons and superconductivity in these noncentrosymmetric superconductors is very small. Thus, we can conclude that a mixing of the spin-singlet and the spin-triplet components in these superconductors is weak and the spin-singlet Cooper pairs dominate. By integrating the Eliashberg spectral function α 2 F (ω), the average electron-phonon coupling parameter λ is obtained to be 0.470 for LaPt 3 Si and 0.488 for LaPtSi 3 , indicating these to be weak-coupling BCS superconductors. Using an acceptable value of µ * = 0.13 for the effective Coulomb repulsion parameter, the superconducting critical temperature T c is calculated to be 0.67 K for LaPt 3 Si and 1.39 K for LaPtSi 3 , in good accordance with experimental values of 0.65 K and 1.52 K, respectively.

Physical properties of hexagonal BaPtAs with noncentrosymmetric SrPtSb-type and centrosymmetric YPtAs-type crystal structures: Effects of spin-orbit coupling

“…1(a)]. A similar observation has been made for the noncentrosymmetric BaPtSb superconductor [33]. This is not surprising because both centrosymmeric superconductors are isostuctural and isoelectronic to each other.…”

“…Explicitly, from the calculated values of elastic constants in Table II, the above restrictions are all satisfied for both phases, revealing their mechanical stability at zero pressure. Furthermore, for both phases, C 11 and C 33 have larger values than remaining elastic constants which reveals that they are significant incompressible under uniaxial stress along x or z axis.…”

“…Furthermore, they are connected to the thermodynamic properties such as specific heat, thermal expansion, Debye temperature, and melting point. For a hexagonal system, there are five linearly independent single-crystal elastic constants, namely, C 11 , C 12 , C 13 , C 33 , and C 44 . The sixth one C 66 equals to 1 2 (C 11 − C 12 ).…”

“…Recently, the linear response approach and the Migdal-Eliashbergh approach [31][32][33][34] have been combined to probe electron-phonon interaction properties of several BaNiSn 3 -type NCS such as SrAuSi 3 , CaIrSi 3 , LaIrSi 3 , LaPdSi 3 , LaRhSi 3 , and LaPtSi 3 . The results of these theoretical studies [31][32][33][34] reveal that the impact of SOC on the electron-phonon interaction in these NCSs is little due to the weak effect of this coupling on their electronic band structures near the Fermi level. Furthermore, first-principles pseudopotential calculations [35] have been carried out to investigate the effect of SOC on superconductivity in the noncentrosymmetric BaPtSb superconductor.…”

Optical study on electronic structure of the locally non-centrosymmetric CeRh$_2$As$_2$

“…4. The SO splitting is much smaller than that of LaPt 3 Si [32] and BiTeI [23]. The different SO splitting size probably originate from the different orbital moments (4d for Rh, 5d for Pt, and 6p for Bi), locally/globally non-centrosymmetric crystal structure, and/or the different dimensionality, three-dimensional LaRh 2 As 2 and LaPt 3 Si, and two-dimensional BiTeBr.…”