  The behavior of Fano resonance and the reversal of near field optical binding
force of dimers over different substrates have not been studied so far. In this
work, we observe that if the closely located plasmonic cube homodimers over
glass or high permittivity dielectric substrate are illuminated with plane wave
polarized parallel to dimer axis, no reversal of optical binding force occurs.
But if we apply the same set-up over a plasmonic substrate, stable Fano
resonance occurs along with the reversal of near field binding force. It is
observed that during such Fano resonance stronger coupling occurs between the
dimers and plasmonic substrate along with the strong enhancement of the
substrate current. Such near field binding force reversals of plasmonic cube
dimers have been explained based on the observed unusual behavior of optical
Lorentz force during the induced stronger Fano resonance and the dipole-dipole
resonance. Although previously reported reversals of near field optical binding
forces were highly sensitive to particle size/shape (i.e. for heterodimers) and
inter-particle distance, our configuration provides much relaxation of those
parameters and hence should be verified experimentally with simpler
experimental set-ups.
