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The Origin of Optical Contrast in Sb 2 Te 3 ‐Based Phase‐Change Materials
Author(s) -
Martinez Jose C.,
Lu Li,
Ning Jing,
Dong Weiling,
Cao Tun,
Simpson Robert E.
Publication year - 2020
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201900289
Subject(s) - condensed matter physics , atomic orbital , materials science , band gap , amorphous solid , electric field , valence (chemistry) , dielectric , electronic structure , orbital hybridisation , phase transition , optics , crystallography , chemistry , physics , valence bond theory , optoelectronics , electron , quantum mechanics
The optical contrast between the crystalline and amorphous forms of phase‐change materials (PCMs) is so marked as to make it ideal for data storage. Various explanations have been given, including smearing of bands, changes in the local structural order and bonding, and resonant bonding. A consensus has not been reached. Herein, the dielectric function of crystalline and amorphous Sb 2 Te 3 , a topological insulator and prototype PCM, is studied using density functional theory and ellipsometry measurements; an expression for interplay between the crystalline electric field and the spin–orbit interaction on the valence band orbitals is derived. It is found that the crystalline electric field and spin–orbit interaction are responsible for this difference and the unusually large refractive index in the crystalline phase. Upon amorphization, a second‐order electronic phase transition is induced by the spin–orbit interaction's effect on the p z orbitals. This mechanism explains how a substantial optical gap can open in systems that have a small electronic band gap.