All-optical phase-change memory in a single nanoparticle

Conventional electronic memories face a challenge in the reduction of size and power consumption as required for meeting the future demand on data storage and access. Phase-change memories have been suggested as candidates for solving this issue, with data recording done by switching the material between an amorphous and a crystalline phase, much in line with today's DVD/DVR technology for optical recording, and even the writing of individual dislocations has been reported. However, polymorphic systems exist in which other crystalline-to-crystalline transitions can provide for higher base logics. Here we demonstrate the principle of a four-level optical memory element obtained by using the phase of a single gallium nanoparticle of 80 nm size, with the four logical states of the memory written by optical pulses of a few pJ energy. The quaternary-logical memory element we demonstrate is comparable in size with the next-generation data storage elements and radically smaller than previously employed diffraction-limited optical memory elements. In addition, the energy required for switching the logical state of the nanoparticle is found to be one order of magnitude less than that of writing a bit in today's DVD/DVR or hard disk technology. This novel principle of operation has implications not only to optical memories and switching, but equally well applies as a key element for achieving plasmonic switching