Tunable Transport in Pd,Pt-based Delafossites via B-site Substitution (Co → Al, Ga, In)

Among delafossites, PdCoO₂ and PtCoO₂ have emerged as leading candidates for next-generation metallic interconnects owing to their exceptionally long mean free paths and ultralow resistivity. A key limitation is the Co 3d admixture near the Fermi level, which perturbs the orbital–momentum texture of the Pd/Pt layers, opens additional scattering channels, and constrains further conductivity gains. We show that B-site engineering—substituting low-spin Co³⁺ (d⁶) with trivalent main-group cations (Al/Ga/In)—systematically suppresses B-site d-state mixing around the Fermi level and thereby enhances the Fermi velocity dominated by the noble-metal triangular layers. Transport analysis indicates that electron-phonon scattering remains nearly unchanged, while the reduced Co-derived contribution lowers the spin-mixing parameter near the Fermi level, decreasing the fraction of SOC-induced spin-flip scattering. Within the Elliott–Yafet framework, this leads to an increase in the spin relaxation time and an extended spin diffusion length. These findings establish B-site substitution in Pd/Pt delafossites as a practical design route to low residual resistivity and long spin diffusion lengths, enabling low-loss interconnects and spin-transport devices without compromising charge transport.