Compositional asymmetry drives directionally biased hot-carrier flow in Pd–Au–Pt plasmonic nanostructures

Understanding how compositional asymmetry influences plasmon-driven charge dynamics is essential for designing efficient plasmonic nanostructures. Here, we use first-principles real-time time-dependent density functional theory (RT-TDDFT) to study hot-carrier generation and coherent charge oscillations in Pd-Au-Pt heterostructures. By comparing symmetric (Pd-Au-Pd, Pt-Au-Pt) and asymmetric (Pd-Au-Pt) stacks, we show that terminal-metal composition controls plasmon lifetimes, spatial charge localization, and the energy distribution of hot carriers. Pd-terminated systems support long-lived collective modes, whereas Pt-terminated structures exhibit rapid damping dominated by interband transitions. Importantly, the asymmetric Pd-Au-Pt stack displays a finite field-even component in the optically driven current-a bias-free, directionally biased ultrafast charge displacement absent in the symmetric controls. This effect arises from broken inversion symmetry at the 1-2 nm scale and occurs within the coherent electron-dynamics regime. These findings highlight atomic-level compositional design as a route to controlling plasmonic response and directional hot-carrier motion for nanoscale energy conversion applications.