Reversible optical binding force in a plasmonic heterodimer under radially polarized beam illumination.

We investigated the optical binding force in a plasmonic heterodimer structure consisting of two nano-disks. It is found that when illuminated by a tightly focused radially polarized beam (RPB), the plasmon modes of the two nano-disks are strongly hybridized, forming bonding/antibonding modes. An interesting observation of this setup is that the direction of the optical binding force can be controlled by changing the wavelength of illumination, the location of the dimer, the diameter of the nano-disks, and the dimer gap size. Further analysis yields that the inhomogeneous polarization state of RPB can be utilized to readily control the bonding type of plasmon modes and distribute the underlying local field confined in the gap (the periphery) of the dimer, leading to a positive (negative) optical binding force. Our findings provide a clear strategy to engineer optical binding forces via changes in device geometry and its illumination profile. Thus, we envision a significant role for our device in emerging nanophotonics structures.