Surface structure and stacking of the commensurate $\left(\sqrt{13}\times \sqrt{13}\right)$R13.9° charge density wave phase of 1T-TaS${}_2$(0001)

Abstract

By quantitative low-energy electron diffraction (LEED) we investigate the extensively studied commensurate charge density wave (CDW) phase of trigonal tantalum disulphide (1T-TaS${}_2$), which develops at low temperatures with a $\left(\sqrt{13}\times \sqrt{13}\right)$R13.9° periodicity. A full-dynamical analysis of the energy dependence of diffraction spot intensities reveals the entire crystallographic surface structure, i.e. the detailed atomic positions within the outermost two trilayers consisting of 78 atoms as well as the CDW stacking. The analysis is based on an unusually large data set consisting of spectra for 128 inequivalent beams taken in the energy range 20-250 eV and an excellent fit quality expressed by a bestfit Pendry R-factor of R=0.110. The LEED intensity analysis reveals that the well-accepted model of star-of-David-shaped clusters of Ta atoms for the bulk structure also holds for the outermost two TaS${}_2$ trilayers. Specifically, in both layers the clusters of Ta atoms contract laterally by up to 0.25 $\mathring{A}$ and also slightly rotate within the superstructure cell, causing respective distortions as well as heavy bucklings (up to 0.23 $\mathring{A}$) in the adjacent sulphur layers. Most importantly, our analysis finds that the CDWs of the 1${}^{\text{st}}$ and 2${}^{\text{nd}}$ trilayer are vertically aligned, while there is a lateral shift of two units of the basic hexagonal lattice (6.71 $\mathring{A}$) between the 2${}^{\text{nd}}$ and 3${}^{\text{rd}}$ trilayer. The results may contribute to a better understanding of the intricate electronic structure of the reference compound 1T-TaS${}_2$ and guide the way to the analysis of complex structures in similar quantum materials.

18 pages, 13 figures

References in corpus (2)

• Gate-tunable Phase Transitions in 1T-TaS${}_2$
• Atomic Lattice Disorder in Charge Density Wave Phases of Exfoliated Dichalcogenides (1T-TaS2)

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• Evidence for reduced periodic lattice distortion within the Sb-terminated surface layer of the kagome metal CsV${}_3$Sb${}_5$
• Behavior under magnetic field of resonance at the edge of the upper Hubbard band in 1T-TaS2
• Topical review: the nature of the ground state and possibility of a quantum spin liquid in 1T metal dichalcogenides
• Electronic Coherence Evolution at the Nearly Commensurate Incommensurate CDW Boundary of 1T-TaS2