Nanoscale active devices, such as all-optical modulators and electro-optical transducers, can be enabled by integrating plasmonic nanostructures with functional materials. Vanadium dioxide (VO), a strongly-correlated electron material, is appealing for active plasmonic applications because its reversible insulator-to-metal transition (IMT) is accompanied by large changes in its electronic and optical properties. Here we exhibit all-optical control of the localized surface plasmon resonance (LSPR) in Au nanoparticles lithographically patterned in an array on a thin VO film.
In our experiment, periodic arrays of Au nanodisks of varying diameters were fabricated lithographically on a 50 nm thick VO thin-film. The Au nanoparticles were arranged in a square lattice with a nominal period much shorter than the wavelength of interest in order to avoid diffraction effects in transmission measurements. Extinction spectra were acquired using an inverted optical microscope integrated with a Fourier-transform infrared spectrometer. By heating or cooling the VO film, the Au plasmon response to ultraviolet light pulses during the IMT was effectively pinned to a strongly correlated state of the VO. Persistent, non-volatile blue-shifting and optical tuning of the LSPR was observed when the array was illuminated by successive ultraviolet-light pulses throughout the temperature range corresponding to the hysteresis of the film.
Control experiments at temperatures above and below the region of strong correlation in the VO, on the other hand, showed no plasmonic tuning effect. The blue-shifted, persistent response of the LSPR appears to be an all-optical analog of the memory capacitance and the memristive response of VO in electronic circuits. This demonstration of a persistent optical resonance controlled in nanometer-scale plasmonic structures opens the door to the studies of other hybrid material systems in which plasmons are coupled to strongly correlated electron materials.