Modelling spin-orbitronics effects at interfaces and chiral molecules

Abstract

Using orbital angular momentum (OAM) currents in nanoelectronics, for example, for magnetization manipulation via spin-orbit torque (SOT), represents a growing field known as "spin-orbitronics". Here, using the density functional theory (DFT) and the real-time dynamics of electronic wave packets, we explore a possibility of generation and propagation of orbital currents in two representative systems: an oxidized Cu surface (where large OAMs are known to form at the Cu/O interface) and a model molecular junction made of two carbon chains connected by a chiral molecule. In the Cu/O system, the orbital polarization of an incident wave packet from the Cu lead is strongly enhanced at the Cu/O interface but then rapidly decays in the bulk Cu due to orbital quenching of asymptotic bulk states. Interestingly, if a finite transmission across the oxygen layer is allowed (in a tunnel junction geometry, for example), a significant spin-polarization of transmitted (or reflected) currents is instead predicted which persists at a much longer distance and can be further tuned by an applied in-plane voltage. For the molecular junction, the mixing of the carbon $p_x$ and $p_y$ (degenerate) channels by the chiral molecular orbital gives rise not only to an efficient generation of orbital current but also to its long-range propagation along the carbon chain.