Spontaneous symmetry breaking in two coupled nanomechanical electron shuttles

We present spontaneous symmetry breaking in a nanoscale version of a setup prolific in classical mechanics: two coupled nanomechanical pendula. The two pendula are electron shuttles fabricated as nanopillars and placed between two capacitor plates in a homogeneous electric field. Instead of being mechanically coupled through a spring they exchange electrons, i.e., they shuttle electrons from the source to the drain "capacitor plate." The nonzero dc current through this system by external ac excitation is caused via dynamical symmetry breaking. This symmetry-broken current appears at sub- and superharmonics of the fundamental mode of the coupled system.