Disorder-induced structural transitions in topological insulating Ge-Sb-Te compounds

Abstract

The mechanism for the fast switching between amorphous, metastable, and crystalline structures in chalcogenide phase-change materials has been a long-standing puzzle. Based on first-principles calculations, we study the atomic and electronic properties of metastable Ge2Sb2Te5 and investigate the atomic disorder to understand the transition between crystalline hexagonal and cubic structures. In addition, we study the topological insulating property embedded in these compounds and its evolution upon structural changes and atomic disorder. We also discuss the role of the surface-like states arising from the topological insulating property in the metal-insulator transition observed in the hexagonal structure.

Effect of vacancy disorder in phase-change materials

“…One essential feature of the PCMs that governs the materials property is the significant amount of vacancies at the 4(b) (cation) sites. The structural stability [31], crystallization speed [32], band topology [33], and transport properties [34][35][36][37] of GST are found to be sensitive to the vacancy distribution. There have been several experimenal reports on the effect of cation and vacancy disorders in GST, in particular, associated with the metal-insulator transition [38] or structural transitions [39,40].…”

Solid-phase equilibria in the GeBi2Te4-Bi2Te3-Te system and thermodynamic properties of compounds of the GeTe·mBi2Te3 homologous series

“…After the discovery of a new quantum state of matter -a topological insulator (TI) [11,12], it was defined that these compounds exhibit the properties of threedimensional TIs and are very upcoming for a variety of applications, including spintronics, quantum computers, medicine, security systems, etc. [13][14][15][16][17][18][19][20][21].…”

Intermixing suppression through the interface in GeTe/Sb2Te3 superlattice

“…On the other hand, it is theoretically known that both inverted-Petrov and Ferro phases in iPCM are topologically non-trivial, and the former is a Dirac semimetal and the latter is a Weyl semimetal, respectively. 22,23) In particular, the Ferro phase breaks spatial inversion symmetry, causing the degenerated electron bands to lift-off and become magnetically sensitive. The new functionalities emerged in phase change memory has attracted attention from spintronics perspective.…”

“…In addition, the element must not break the topological symmetry (time-reversal), realizing a large resistance difference. 23) Moreover, the element must not prevent Ge atomic switching between the inverted-Petrov and Ferro phases. From all these reasons, the fourth element must be chalcogenide, S or Se.…”