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Role of vacancies in metal–insulator transitions of crystalline phase-change materials

Abstract

The study of metal–insulator transitions (MITs) in crystalline solids is a subject of paramount importance, both from the fundamental point of view and for its relevance to the transport properties of materials. Recently, a MIT governed by disorder was observed in crystalline phase-change materials. Here we report on calculations employing density functional theory, which identify the microscopic mechanism that localizes the wavefunctions and is driving this transition. We show that, in the insulating phase, the electronic states responsible for charge transport are localized inside regions having large vacancy concentrations. The transition to the metallic state is driven by the dissolution of these vacancy clusters and the formation of ordered vacancy layers. These results provide important insights on controlling the wavefunction localization, which should help to develop conceptually new devices based on multiple resistance states.

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Figure 1: Local density of p states (LDOS) on the 500 Te sites in a Ge125Sb250Te500 supercell.
Figure 2: Total energy per atom, Ediff, of the models of cubic GST, hexagonal GST and intermediate structures studied.
Figure 3: Localization properties of the electronic states of some of the models studied.

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Acknowledgements

We thank S. Caravati and Y. Li for useful discussions. We gratefully acknowledge funding by the DFG (German Science Foundation) within the collaborative research centre SFB 917 ‘Nanoswitches’, as well as the computational resources by the RWTH Rechenzentrum and the Forschungszentrum Jülich.

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W.Z. and A.T. performed the CP2K and KKRNano simulations respectively. Analysis of the data was mostly carried out by W.Z., P.Z. and R.M. (CP2K) and A.T., R.Z. and P.H.D. (KKRnano). The paper was written by R.M. and M.W., with help from all co-authors, in particular W.Z. and A.T. The project was initiated and conceptualized by S.B., R.M. and M.W.

Corresponding authors

Correspondence to M. Wuttig or R. Mazzarello.

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The authors declare no competing financial interests.

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Zhang, W., Thiess, A., Zalden, P. et al. Role of vacancies in metal–insulator transitions of crystalline phase-change materials. Nature Mater 11, 952–956 (2012). https://doi.org/10.1038/nmat3456

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