Hopping of nanoparticles in optical tweezers governed by Mie resonances
Optical tweezers have become a standard tool for manipulating microscale and nanoscale particles and probing their local environments. However, complex particle dynamics under optical forces typically require structured light fields, multi-beam traps, or engineered environments. Here we achieve complex particle dynamics in a single Gaussian-beam optical tweezer. The effect originates from higher-order Mie resonances supported by wavelength-scale particles. In our optical tweezer, small particles in the regime of Rayleigh scattering or the lowest-order dipole-type Mie modes remain confined at the beam center. By contrast, particles within the range of sizes corresponding to quadrupole-type Mie modes exhibit more complex behavior. In a linearly polarized Gaussian beam, these particles are trapped in a potential with two off-axis equilibria. We observe thermally driven hopping between these equilibria, with the hopping frequency controlled by the laser power. In a circularly polarized Gaussian beam, the particles are confined to a stable orbit and exhibit circular motion driven by the spin (circular-polarization) degree of freedom of the beam, with angular velocity dependent on the laser power. These results reveal higher-order Mie resonances as an intrinsic mechanism behind complex optical forces. This establishes Mie-resonant nanophotonics as a flexible platform for inducing and controlling complex motion in optical tweezers for nanoparticle manipulation as well as sensing of local environments.