A remarkable match of optical response in the amorphous-crystalline and zinc blende-rock salt phase pairs of GeTe

Abstract

Despite a large amount of theoretical and experimental work performed so far, the search of Phase Change Materials (PCM) is done with use of numerical modeling. However, it is not fully clear how and why the phase change translates into the optical contrast. In this work, we argue that a key prerequisite for a material to have a pronounced difference in optical properties between crystalline and glassy phases of PCM is the similar contrast between the observed crystalline and (may be experimentally inaccessible) parent crystalline polymorph of the glassy phase. To illustrate this claim, we report a comparison of dynamic dielectric function of zinc-blende (a-ZnS), CsCl, and rocksalt (NaCl) phases of the binary AIVBVI PCM exemplified by the well known GeTe prototype compound with experimental data and supply a theoretical explanation to the observed behavior based on topological properties of the Fermi surfaces appearing in the protoptypic “degenerate” crystals with A=B having the same local structure as the parent polymorphs and derived from simple analytical model. By this, we arrive to a qualitative rather than purely numeric guidance for possible search of the novel phase-change materials.