Motion bistability of the plasmon nanoaggregate due to the light induced interparticle forces

The optical forces between coupled metal nanoparticles are strongly enhanced by high field gradients that is currently of great interest for nanoscale optical manipulation such as "optical nanotweezers". A special case arises when the light induced forces are comparable with the relatively weak forces, such as the dispersion ones, as well as the electrostatic forces. This is valid, in particular, for plasmonic aggregates in solution or those assembled by molecules. In this situation the optical forces can significantly shift the mechanical equilibrium of the nanoaggregate. As it was shown recently, the feedback between the light-induced motion of the particles and their optical response results in an optical nonlinearity of the aggregate, even if all materials have purely linear optical response. Here we show that particles mutual motion results in an optical bistability for the aggregate of metal nanoparticles.