Ferroelectric catastrophe: beyond nanometre-scale optical resolution

摘要

The optical diffraction limit is rigidly determined as a simple equation of wavelength lambda and lens numerical aperture NA (<=1): lambda/2/NA. In this paper, we report that Ag_(5.8)In_(4.4)Sb_(61.0)Te_(28.8) and Ge_2Sb_2Te_5 chalcogenide thin films, which are typical of optical recording materials used in digital versatile discs (DVDs), enable a resolution of under lambda/10 due to their ferroelectric properties. In the Ag_(5.8)In_(4.4)Sb_(61.0)Te_(28.8) film it was found that this optical super-resolution can be observed between 350 and 400 deg C, resulting in a second phase transition from a hexagonal (A7 belonging to R3-barm) to a rhombohedral structure of R32 or R3m. In Ge_2Sb_2Te_5, on the other hand, the temperature range is much wider, between 250 and 450 deg C, which is also due to a second phase transition from a NaCl-type fcc to a hexagonal structure.