The success of semiconductor electronics is built on the creation of compact, low-power switching elements that offer routing, logic, and memory functions. The availability of nanoscale optical switches could have a similarly transformative impact on the development of dynamic and programmable metasurfaces, optical neural networks, and quantum information processing. Phase change materials are uniquely suited to enable their creation as they offer high-speed electrical switching between amorphous and crystalline states with notably different optical properties. Their high refractive index has also been harnessed to fashion them into compact optical antennas. Here, we take the next important step by realizing electrically-switchable phase change antennas and metasurfaces that offer strong, reversible, non-volatile, multi-phase switching and spectral tuning of light scattering in the visible and near-infrared spectral ranges. Their successful implementation relies on a careful joint thermal and optical optimization of the antenna elements that comprise an Ag strip that simultaneously serves as a plasmonic resonator and a miniature heating stage.

Glass forming materials are employed in information storage technologies making use of the transition between a disordered (amorphous) and an ordered (crystalline) state. With increasing temperature the crystal growth velocity of these phase-change materials becomes so fast that prior studies have not been able to resolve these crystallization dynamics. However, crystallization is the time limiting factor in the write speed of phase-change memory devices. Here, for the first time, we quantify crystal growth velocities up to the melting point by using the relaxation of photo-excited carriers as an ultrafast heating mechanism.During repetitive femtosecond optical excitation, each pulse enables dynamical evolution for tens of picoseconds before the intermediate atomic structure is frozen-in as the sample rapidly cools. We apply this technique to Ag 4 In 3 Sb 67 Te 26 (AIST) and compare the dynamics of as-deposited and application-relevant melt-quenched glass. Both glasses retain their different kinetics even in the supercooled liquid state, thereby revealing differences in their kinetic fragilities. This approach enables the characterization of application-relevant properties of phase-change materials up to the melting temperature, which has not been possible before.Mankind has utilized glasses during the last five thousand years. They can be prepared by cooling a liquid fast and far enough below the glass transition temperature -to a temperature where its viscosity is sufficiently high that the atomic arrangement is kinetically frozen-in 1 . Until recently, research and technology have focused on good glass formers, i.e. materials which can be vitrified by cooling their liquid state at moderate rates. But in recent decades poor glass formers such as metallic glasses and certain chalcogenide glasses have gained interest due to their remarkable property portfolio 2,3 . These materials need to be cooled at rates in excess of around 3*10 9 K/s to bypass crystallization and to quench the atoms in an amorphous arrangement 4 . This so-called glass transition at temperature is commonly observed at a

Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag_{4}In_{3}Sb_{67}Te_{26}. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales-faster than crystals can nucleate. This supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch.

We show that a dielectric nanowire (NW) with a rectangular cross section can effectively be modeled as a Fabry-Perot cavity formed by truncating a dielectric slab waveguide. By calculating the mode indices of the supported waveguide modes and the reflection phase pickup of the guided waves from the end facets, we can numerically predict the spectral locations of optical, Mie-like resonances for such NWs. This type of analysis must be performed twice in order to account for all resonances of these structures, corresponding to light propagating in the vertical or horizontal directions. The model shows excellent agreement with full-field simulations. We show how the refractive index of both the NW itself and neighboring materials and substrates impact the resonant properties. Our results can aid the development of NW-based optoelectronic devices, for which rectangular cross sections are much simpler to fabricate using top-down fabrication procedures.

The increased importance of plasmonic devices has prompted a sizable research activity directed toward the development of ultracompact and high-performance couplers. Here, we present a novel scheme for efficient, highly localized, and directional sourcing of surface plasmon polaritons (SPPs) that relies on the excitation of leaky mode optical resonances supported by high-refractive index, semiconductor nanowires. High coupling efficiencies are demonstrated via finite difference frequency domain simulations and experimentally by leakage radiation microscopy. This efficiency is quantified by means of a coupling cross section, the magnitude of which can exceed twice the geometric cross section of the nanowire by exploiting its leaky resonant modes. We provide intuition into why the SPP coupling via certain wire modes is more effective than others based on their symmetry properties. Furthermore, we provide an example showing that dielectric scatterers may perform as well as metallic scatterers in coupling to SPPs.