Switchable Optical Trapping of Mie-Resonant Phase-Change Nanoparticles

Optical tweezers revolutionized the manipulation of nanoscale objects. Typically, tunable manipulations of optical tweezers rely on adjusting either the trapping laser beams or the optical environment surrounding the nanoparticles. Here, tunable and switchable trapping using nanoparticles made of a phase-change material (vanadium dioxide or VO₂) are achieved. By varying the intensity of the trapping beam, transitions of the VO₂ between monoclinic and rutile phases are induced. Depending on the nanoparticles' sizes, they exhibit one of three behaviors: small nanoparticles (in the settings, radius (Formula presented.) wavelength (Formula presented.)) remain always attracted by the laser beam in both material phases, large nanoparticles ((Formula presented.)) remain always repelled. However, within the size range of (Formula presented.), the phase transition of the VO₂ switches optical forces between attractive and repulsive, thereby pulling/pushing them toward/away from the beam center. The effect is reversible, allowing the same particle to be attracted and repelled repeatedly. The phenomenon is governed by optical Mie modes of the nanoparticles and their alterations during the phase transition of the VO₂. This work provides an alternative solution for dynamic optical tweezers and paves a way to new possibilities, including optical sorting, light-driven optomechanics and single-molecule biophysics.