Topological superconductivity and large spin Hall effect in the kagome family Ti6X4 (X = Bi, Sb, Pb, Tl, and In)

Topological superconductors (TSC) become a focus of research due to the accom-panying Majorana fermions. However, the reported TSC are extremely rare. Recent experiments reported kagome TSC AV(3)Sb(5) (A = K, Rb, and Cs) exhibit unique superconductivity, topological surface states (TSS), and Majorana bound states. More recently, the first titanium-based kagome superconductor CsTi3Bi5 with nontrivial topology was successfully synthesized as a perspective TSC. Given that Cs contributes little to electronic structures of CsTi3Bi5 and binary com-pounds may be easier to be synthesized, here, by first-principle calculations, we predict five stable nonmagnetic kagome compounds Ti6X4 (X = Bi, Sb, Pb, Tl, and In) which exhibit superconductivity with critical temperature Tc = 3.8 K -5.1 K, nontrivial 7L2 band topology, and TSS close to the Fermi level. Addition-ally, large intrinsic spin Hall effect is obtained in Ti6X4 , which is caused by gapped Dirac nodal lines due to a strong spin-orbit coupling. This work offers new plat-forms for TSC and spintronic devices.