Charge-to-spin conversion in epitaxial and polycrystalline Bi and Bi/Ag layers

Bismuth is a promising spin current generator owing to its strong spin--orbit coupling, spin-polarized surface states, and large intrinsic spin Hall conductivity predicted by theory. Yet experimental reports of spin--charge interconversion efficiencies remain remarkably inconsistent. The authors compare structural, spectroscopic, and spin--orbit torque measurements of epitaxial and polycrystalline Bi layers in combination with different metal spacers and ferromagnets. The results reveal extensive interdiffusion and dewetting unless Ag overlayers are used to preserve the structural and chemical integrity of Bi, unlocking a giant bulk spin Hall angle exceeding unity and highlighting the potential of Bi for spintronic applications.