Evidence for topological band inversion of the phase change material Ge2Sb2Te5

Pauly, Christian; Liebmann, Marcus; Giussani, A.; Kellner, Jens; Just, Sven; Sánchez-Barriga, J.; Rienks, E.; Rader, O.; Calarco, Raffaella; Bihlmayer, Gustav; Morgenstern, Markus

doi:10.1063/1.4847715

Cited by 29 publications

(50 citation statements)

References 43 publications

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“…XRD reveals that the GST-225 films grow epitaxially exhibiting the single crystalline, metastable phase with [111] surface. Twin domains are deduced from XRD, i.e., adjacent areas of ABC and CBA stacking of the hexagonal layers [35]. The samples on the Si(111)-7 × 7 reconstruction additionally feature rotational domains.…”

Section: Sample Preparation and Stm/sts Experimentsmentioning

confidence: 99%

“…• C [21,22,35]. The substrates are primarily prepared to reveal the Si(111)-7 × 7 reconstruction or the Si(111) √ 3 × √ 3-Sb reconstruction using slightly different protocols for substrate preparation [50].…”

Section: Sample Preparation and Stm/sts Experimentsmentioning

confidence: 99%

“…This more ordered phase deviates from the rocksalt structure and has recently been dubbed the metastable vacancy-ordered phase [28]. Moreover, it is known that the epitaxial films are strongly p-type doped [35] with an unintentionally varying charge carrier density p = (0.1-3) × 10 26 m −3 [24,26]. This doping is typically related to excess vacancies [36][37][38].…”

Section: Introductionmentioning

confidence: 99%

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Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

et al. 2017

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Scanning tunneling microscopy (STM) and spectroscopy (STS) in combination with density functional theory (DFT) calculations are employed to study the surface and subsurface properties of the metastable phase of the phase-change material Ge 2 Sb 2 Te 5 as grown by molecular beam epitaxy. The (111) surface is covered by an intact Te layer, which nevertheless permits the detection of the more disordered subsurface layer made of Ge and Sb atoms. Centrally, we find that the subsurface layer is significantly more ordered than expected for metastable Ge 2 Sb 2 Te 5 . First, we show that vacancies are nearly absent within the subsurface layer. Secondly, the potential fluctuation, tracked by the spatial variation of the valence band onset, is significantly less than expected for a random distribution of atoms and vacancies in the subsurface layer. The strength of the fluctuation is compatible with the potential distribution of charged acceptors without being influenced by other types of defects. Thirdly, DFT calculations predict a partially tetrahedral Ge bonding within a disordered subsurface layer, exhibiting a clear fingerprint in the local density of states as a peak close to the conduction band onset. This peak is absent in the STS data implying the absence of tetrahedral Ge, which is likely due to the missing vacancies required for structural relaxation around the shorter tetrahedral Ge bonds. Finally, isolated defect configurations with a low density of 10 −4 nm −2 are identified by comparison of STM and DFT data, which corroborates the significantly improved order in the epitaxial films driven by the buildup of vacancy layers.

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Section: Sample Preparation and Stm/sts Experimentsmentioning

confidence: 99%

Section: Sample Preparation and Stm/sts Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

et al. 2017

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“…8 Our calculations suggest that cationic disorder by Ge-Sb exchange affects mostly the low energy states near the Fermi level and eventually induces formation of the topological insulating phase in our cubic GST225. 13 This trend demonstrates that the disorder not only affects the electronic band structure but also can control its topological nature. These observations in turn imply that metastable cubic GST may have different topological phases controlled by the degree of disorder, which can be exploited to realize multilevel states.…”

Section: Resultsmentioning

confidence: 99%

“…[8][9][10] Experimental observation of weak antilocalization in GeSb 2 Te 4 , angle-resolved photoemission study for Ge 2 Sb 2 Te 5 (GST225), and large magneto-resistance in interfacial PCMs supports these theoretical predictions. [11][12][13] GST225 undergoes a series of structural transitions from amorphous to metastable rock-salt structure (or cubic) at $150 C and then to stable hexagonal structure at >300 C. 14 For the hexagonal structure, three types of layer sequencing have been suggested: Petrov sequence Te-Sb-TeGe-Te-Te-Ge-Te-Sb-, 15 Kooi and De Hosson (KH) sequence Te-Ge-Te-Sb-Te-Te-Sb-Ge-, 16 and intermixed sequence TeGe/Sb-Te-Te-Sb/Ge-. 17 According to first-principles calculations, the KH sequence is slightly more stable than the Petrov and intermixed sequences.…”

Section: Introductionmentioning

confidence: 99%

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

Kim

Jhi

2015

Journal of Applied Physics

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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.

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Microscopic Complexity in Phase‐Change Materials and its Role for Applications

Deringer

Dronskowski

Wuttig

2015

Adv Funct Materials

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Phase‐change materials (PCMs) are widely used for data storage and in other functional devices. Despite their seemingly simple compositions, these materials exhibit intriguing microscopic complexity and a portfolio of interesting properties. In this Feature Article, it is shown that structural and electronic peculiarities on the atomic scale are key determinants for the technological success of PCMs. Particular emphasis is put on the interplay of different experimental and theoretical methods, on the bonding nature of crystalline and amorphous PCMs, and on the role of surfaces and nanostructures. Then, unconventional transport properties of the crystalline phases are highlighted, both with regard to electrical and heat conduction. Finally, perspectives and future directions are drawn: for finding new PCMs based on microscopic understanding, and also for new applications of these materials in emerging fields.

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Evidence for topological band inversion of the phase change material Ge2Sb2Te5

Cited by 29 publications

References 43 publications

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

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

Microscopic Complexity in Phase‐Change Materials and its Role for Applications

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