  We harness non-volatile, amorphous-crystalline transitions in the
chalcogenide phase-change medium germanium antimony telluride (GST) to realize
optically-switchable, all-dielectric metamaterials. Nanostructured,
subwavelength-thickness films of GST present high-quality resonances that are
spectrally shifted by laser-induced structural transitions, providing
reflectivity and transmission switching contrast ratios of up to 5:1 (7 dB) at
visible/near-infrared wavelengths selected by design.
