Density Functional Theory Analysis of the Non-Centrosymmetric Superconductors TaRuSi and TaReSi

The non-centrosymmetric superconductors TaRuSi and TaReSi are studied within density functional theory (DFT). We have quantified the strength of spin-orbit coupling (SOC) through an analysis of the DFT band structure showing strong SOC in TaReSi and weak SOC in TaRuSi. A recent symmetry analysis suggests that time-reversal symmetry (TRS) breaking in the superconducting state for materials with the crystallographic point group of TaRuSi and TaReSi is possible only in the limit of weak SOC. In light of our DFT calculations, this indicates that TRS breaking may only be observed in the superconducting state of TaRuSi. Furthermore, the TRS broken superconducting state is expected to arise from a non-unitary triplet-pairing mechanism. Muon spin spectroscopy measurements for TaRuSi and TaReSi reveal TRS breaking in TaRuSi in the superconducting state while TRS is preserved in TaReSi, in agreement with the results of symmetry analysis and DFT calculations. Measurements also provide evidence for multigap s+d-wave superconductivity in TaRuSi. I will present the results of DFT calculations showing the effects of SOC on the electronic band structure and Fermi surfaces of TaRuSi and TaReSi.