Large Intrinsic Spin Hall Effect in the A15 Superconductor Family: A Topology and Symmetry based Design Strategy

The spin Hall effect (SHE) is the conversion of a charge current to a spin current and non-magnetic metals with a large SHE are useful for a variety of spintronic applications, but their rarity has stifled their widespread use. Here we predict the presence of a large intrinsic SHE in the A15 family of superconductors: Ta_3Sb, Nb_3Au, and Cr_3Ir having spin hall conductivities of -1400, -1060, and 1210 hbar/e*(Omega*cm)^-1, respectively. Combining concepts from topological physics with the dependence of the SHE on the Berry curvature of the Fermi surface, we propose a simple strategy to design materials with a large intrinsic SHE based on the following ideas: that high symmetry combined with heavy atoms can give rise to multiple Dirac/Weyl crossings, that these crossings can gap due to spin orbit coupling without sufficient symmetry protection, and that gapped Dirac/Weyl crossings can create a large Berry curvature. We use these to explain why beta-W and Pt have a large intrinsic SHE and present a family of sputterable, large SHE compounds and alloys (e.g. W_3Ta, 2250). This represents the first application of topological physics in state of the art technology and, with tuning of extrinsic parameters, will represent a new direction in the route to efficient charge/spin conversion.