Nanoscale optical switching of photochromic material by ultraviolet and visible plasmon nanofocusing

Optical control of electronic properties is essential for future electric devices. Manipulating such properties has been limited to the microscale in spatial volume due to the wave nature of light; however, scaling down the volume is in extremely high demand. In this study, we demonstrate optical switching within a nanometric spatial volume in an organic electric material. Photochromic materials such as diarylethene derivatives exhibit semiconducting and insulating properties on ultraviolet (UV) and visible light, respectively, which are promising for optical switching and memory. To control the wavelength between visible and UV light at the nanoscale, we employed plasmon nanofocusing, which allows the creation of a nanolight source at the apex of a metallic tapered structure over a broad frequency range by focusing of propagating plasmons. We utilized an aluminum tapered structure and realized in-situ wavelength control between visible and UV light at the nanoscale. Using this method, nanoscale optical switching between the two states of diarylethene was demonstrated. The switching performance was confirmed for at least nine cycles without degradation. This demonstration would make a significant step forward toward next-generation nanoscale optoelectronic devices and stimulate diverse scientific fields owing to the unique concept of broadband plasmon nanofocusing.