Phase Transition and Self-Stabilization of Light-Mediated Metal Nanoparticle Assemblies.

Light-mediated self-organization of nanoparticles (NPs) offers a route to study mesoscale electrodynamics interactions in many-body systems. Here we report the phase transition and self-stabilization of dynamic assemblies with up to 101 plasmonic metal NPs in optical fields. The spatial stability of self-organized NPs is strongly influenced by the laser intensity and polarization state, where phase transition occurs when the intensity increases and the polarization changes from linear to circular. Well-organized NP arrays can form in a circularly polarized laser beam, where the center of an array is less susceptible to thermal fluctuations than the edge. Moreover, larger arrays are self-protected from fluctuation-induced instability by incorporating more NP constituents. The dynamics of NP arrays can be understood by electrodynamic simulations coupled with thermal fluctuations and by examining their potential energy surfaces. This study clearly reveals the spatial inhomogeneity of optical binding interactions in a two-dimensional multiparticle system, which is important for building large-scale optical matter assemblies with NPs.