Photoinduced phase transition in VO₂ nanocrystals: Ultrafast control of surface-plasmon resonance

We study the ultrafast insulator-to-metal transition in nanoparticles of VO₂, obtained by ion implantation and self-assembly in silica. The nonmagnetic, strongly correlated compound VO₂ undergoes a reversible phase transition, which can be photoinduced on an ultrafast time scale. In the nanoparticles, prompt formation of the metallic state results in the appearance of surface-plasmon resonance. We achieve large, ultrafast enhancement of optical absorption in the near-infrared spectral region that encompasses the wavelength range for optical-fiber communications. One can further tailor the response of the nanoparticles by controlling their shape.