Enhanced Spin-Orbit Coupling in Heavy Metals via Molecular Coupling

5d metals are used in electronics because of their high spin-orbit coupling (SOC) leading to efficient spin-electric conversion. When C₆₀ is grown on a metal, the electronic structure is altered due to hybridization and charge transfer. In this work, we measure the spin Hall magnetoresistance for Pt/C₆₀ and Ta/C₆₀, finding that they are up to a factor of 6 higher than those for pristine metals, indicating a 20-60% increase in the spin Hall angle. At low fields of 1-30 mT, the presence of C₆₀ increased the anisotropic magnetoresistance by up to 700%. Our measurements are supported by noncollinear density functional theory calculations, which predict a significant SOC enhancement by C₆₀ that penetrates through the Pt layer, concomitant with trends in the magnetic moment of transport electrons acquired via SOC and symmetry breaking. The charge transfer and hybridization between the metal and C₆₀ can be controlled by gating, so our results indicate the possibility of dynamically modifying the SOC of thin metals using molecular layers. This could be exploited in spin-transfer torque memories and pure spin current circuits.