  In general,the optical binding force between identical particles is thought
to be symmetric.However,we demonstrate analytically a counter-intuitively
asymmetric longitudinal optical binding force between two identical dual
dipolar dielectric particles.This homodimer is confined in two
counter-propagating incoherent plane waves along the dimer's axis.The force
consists of the electric dipolar,magnetic dipolar,and electric-magnetic dipolar
coupling interactions.The combined effect of these interactions is markedly
different than the expected behavior in the Rayleigh approximation.The
asymmetric force is a result of the asymmetric forward and backward scattering
of the particles due to the dipolar hybridization and coupling
interactions.Consequently,it leads to a harmonic driving force on the
pair,which decays with the interparticle distance to the first power.We show
the rich nonequilibrium dynamics of the dimer and of the two particles impelled
by the driving and binding forces and discuss the ranges of particle refractive
index and size in which the asymmetric binding force arises.Our results open
perspectives for nonequilibrium light-driven multiparticle transport and
self-assembly.
