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Regensburg 2019 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 87: 2D Materials IV: Charge Density Waves and Electronic Properties

O 87.2: Vortrag

Donnerstag, 4. April 2019, 15:15–15:30, H25

Structure determination of the commensurate charge density wave phase of 1T-TaS2Gevin von Witte1, Tilman Kißlinger2, Jan-Gerrit Horstmann1, Kai Roßnagel3, Alexander Schneider2, Claus Ropers1, and •Lutz Hammer21IV. Phys. Inst., Univ. Göttingen — 2Ls. f. Festkörperphysik, Univ. Erlangen-Nürnberg — 3Inst. f. Exp. u. Angew. Physik, Univ. Kiel

The transition metal dichalcogenide 1T-TaS2 consists of van-der-Waals stacked S–Ta–S trilayers with tetrahedrally coordinated Ta atoms. Depending on temperature several charge-density wave (CDW) states are observed. Here, we present a structural analysis of the low-temperature (√13 × √13)R13.9 CDW-phase (C-phase) by quantitative LEED-IV.

From an UHV-cleaved single crystal, we collected a large total data base comprising 128 inequivalent beams which allows to determine 78 structural parameters safely (redundancy factor ρ = 10). The excellent fit quality achieved is expressed by a Pendry R-factor of RP = 0.12.

The C-phase shows a strongly modulated superstructure with Ta atoms arranged in Star-of-David shaped clusters. LEED-IV reveals that the CDW distortion of the topmost trilayer is practically bulk-like with only tiny vertical atomic relaxations (≤0.06 Å): The clusters of Ta atoms contract laterally by up to 0.25 Å  and also rotate within the superstructure cell, causing respective distortions as well as heavy bucklings (≈0.20 Å) in the adjacent sulphur layers. Most importantly, we find a stacking sequence of A–A–B of the three outermost trilayers, i.e., a vertical stacking of the top trilayer and a shift by two units of the basic hexagonal lattice (6.73 Å) between the 2nd and 3rd layer.

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