Topological properties of Au-based superconducting A15 compounds: Unveiling Dirac surface states and spin Hall effects

Interest in exploring the topological properties of superconducting compounds is growing, as this can provide valuable insights into the realization of topological superconductivity. In this study, we employed first-principles calculations to explore the topological and superconducting properties of X3Au (X=V,Nb,Ta) A15 compounds. Nb3Au is identified as a non-trivial topological metal with a Dirac-like surface state along its (001) surfaces. Furthermore, we calculated the spin Hall conductivity (SHC) for the non-magnetic compounds Nb3Au and Ta3Au, as well as the anomalous Hall conductivity (AHC) for the ferromagnetic V3Au. Their significant SHC and AHC values highlight their potential for spintronic applications. Furthermore, we show multifold topological phonon band features in these compounds, resulting from their nonsymmorphic symmetries. Finally, our calculation of the Eliashberg function of Nb3Au reveals a strong electron–phonon coupling constant (λ=1.74), primarily driven by Nb-based modes, resulting in a critical temperature for superconductivity of 21.8 K. Taken together, our finding of a distinctive Dirac-like surface state coexisting with strong electron–phonon coupling in Nb3Au suggests that this compound is a candidate for hosting topological superconductivity.