Curl maps in nanowires

Abstract

Nonconservative current-induced forces (NCIFs) in nanowires have attracted attention both as a failure mechanism and as a driver for atomic-scale motors. Here we investigate the view that the nonconservative character of the electron wind force is an intrinsic property of the electron flow. To this end we consider the curl of the force on a noninvasive test scatterer immersed in the electron current. Using a free-electron Hamiltonian, we find nonzero curls at the opening of conductance channels due to variations in the local density of states. Current vortices are observed in these simulations, and one would naively expect them to give rise to large curls. However, this is not always the case. We find two types, low- and high-curl current vortices. Bouncy patterns, the `snaking' of the current flow through the wire, are a prominent effect that gives rise to large curls. Ultimately NCIFs reduce the stability of nanowires and therefore it is crucial to study their origin to manage their effects. This approach enhances our understanding of NCIFs by going beyond forces on individual nuclei.