Electronic and lattice properties of non-centrosymmetric superconductors ThTSi (T = Co, Ir, Ni, and Pt)

The theoretical studies on the electronic and lattice properties of the series of non-centrosymmetric superconductors ThTSi, where T = Co, Ni, Ir, and Pt are presented. The electronic band structure and crystal parameters were optimized within the density functional theory. The spin-orbit coupling leads to the splitting of the electronic bands and Fermi surfaces, with the stronger effect observed for the compounds with the heavier atoms Ir and Pt. The possible mixing of the spin-singlet and spin-triplet pairing in the superconducting state is discussed. The phonon dispersion relations and phonon density of states were obtained using the direct method. The dispersion curves in ThCoSi and ThIrSi exhibit the low-energy modes along the S-N-S0 line with the tendency for softening and dynamic instability. Additionally, we calculate and analyse the contributions of phonon modes to lattice heat capacity.