Abstract
The Ge2Sb2Te5 is a phase-change material widely used in optical memory devices and is a leading candidate for next generation non-volatile random access memory devices which are key elements of various electronics and portable systems. Despite the compound is under intense investigation its electronic structure is currently not fully understood. The present work sheds new light on the electronic structure of the Ge2Sb2Te5 crystalline phases. We demonstrate by predicting from first-principles calculations that stable crystal structures of Ge2Sb2Te5 possess different topological quantum phases: a topological insulator phase is realized in low-temperature structure and Weyl semimetal phase is a characteristic of the high-temperature structure. Since the structural phase transitions are caused by the temperature the switching between different topologically non-trivial phases can be driven by variation of the temperature. The obtained results reveal the rich physics of the Ge2Sb2Te5 compound and open previously unexplored possibility for spintronics applications of this material, substantially expanding its application potential.
Highlights
The obtained small band-gap value may be an indication that the system is close to the topological quantum phase transition (TQPT) and can be converted into the topological phase by increasing spin-orbit interaction strength
We artificially increased the spin-orbit interaction strength λ in the ordered equilibrium structure and found that it leads to shift of the gap towards the A point along with its narrowing
Upon further increasing the spin-orbit interaction strength the system has gone through the critical point of the TQPT, the gap becomes inverted achieving at λ/λ0 = 1.4 a width of 76 meV at the A point (Fig. 1(c))
Summary
(e) Bulk band structure of Kooi-Ge2Sb2Te5 with Ge/Sb mixing, and (f) its magnified view near the A-gap with indication of the weights of Te and Ge/Sb pz orbitals (VCA-ABINIT calculation). The calculated bulk band structure demonstrates the insulating state with a gap of 25.2 meV in the middle of the Γ-A direction (Fig. 1(b), red lines) which is trivial band insulator in terms of the 2 topological invariant that is in agreement with earlier results[7,11,12].
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