Simulating bistable current-induced switching of metallic atomic contacts by electron-vibration scattering

Abstract

We present a microscopic model, describing current-driven switching in metallic atomic-size contacts. Applying a high current through an atomic-size contact creates a strong electronic nonequilibrium that excites vibrational modes by virtue of the electron-vibration coupling. Using density-functional theory (DFT) in combination with the Landauer-Büttiker theory for phase-coherent transport, expressed in terms of nonequilibrium Green's functions (NEGFs), we study the current-induced forces arising from this nonequilibrium and determine those vibrational modes which couple most strongly to the electronic system. For single-atom lead (Pb) contacts we show specific candidates for bistable switches, consisting of two similar atomic configurations with differing electric conductance. We identify vibrational modes that induce a transition between these configurations. Our results reveal a possible origin of bistable switching in atomic-size contacts through excitation of vibrations by inelastic electron scattering and underline the power of the combined DFT-NEGF approach and statistical mechanics analysis of a Langevin equation to overcome the timescale gap between atomic motion and rare switching events, allowing for an efficient exploration of the contacts' configurational phase space.