Single-layer TaS 2 is epitaxially grown on Au(111) substrates. The resulting two-dimensional crystals adopt the 1H polymorph. The electronic structure is determined by angle-resolved photoemission spectroscopy and found to be in excellent agreement with density functional theory calculations. The single-layer TaS 2 is found to be strongly n doped, with a carrier concentration of 0.3(1) extra electrons per unit cell. No superconducting or charge density wave state is observed by scanning tunneling microscopy at temperatures down to 4.7 K.

Charge transfers resulting from weak bondings between two-dimensional materials and the supporting substrates are often tacitly associated with their work function differences. In this context, two-dimensional materials could be normally doped at relatively low levels. Here, we demonstrate how even weak hybridization with substrates can lead to an apparent heavy doping, using the example of monolayer 1H-TaS2 grown on Au(111). Ab-initio calculations show that sizable changes in Fermi areas can arise, while the transferred charge between substrate and two-dimensional material is much smaller than the variation of Fermi areas suggests. This mechanism, which we refer to as pseudodoping, is associated with non-linear energy-dependent shifts of electronic spectra, which our scanning tunneling spectroscopy experiments reveal for clean and defective TaS2 monolayer on Au(111). The influence of pseudodoping on the formation of many-body states in two-dimensional metallic materials is analyzed, shedding light on utilizing pseudodoping to control electronic phase diagrams.

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The commensurate charge density wave (CDW) in the layered compound 1T -TaS2 has hitherto mostly been treated as a quasi two-dimensional phenomenon. Recent band structure calculations have, however, predicted that the CDW coexists with a nearly one-dimensional metallic dispersion perpendicular to the crystal planes. Using synchrotron radiation based angle-resolved photoemission spectroscopy, we show that this metallic band does in fact exist. Its occupied band width is in excellent agreement with predictions for a simple τc stacking order of the CDW between adjacent layers and its periodicity in the c direction is 2π/c.The 1T polytype of TaS 2 is one of the most studied layered transition metal dichalcogenides (TMDCs). Its rich electronic phase diagram involves several charge density wave (CDW) transitions driven by strong electronic correlations and electron-phonon coupling [1,2]. Particular focus has been on the ground state below 180 K which is a commensurate CDW phase with a √ 13 × √ 13 socalled Star of David reconstruction that is rotated by 13.9• against the lattice. In this phase, the large-scale periodic lattice distortion is thought to coexist with a Mott insulating ground state arising from the single electron localized on the centre atom of the Star of David [1,3]. While the research on CDWs in layered TMDCs is more than 40 years old, renewed interest has been driven by the possibility to elucidate transitions between different CDW states using ultrafast techniques [4][5][6][7][8][9]; by the observation of metastable "hidden states" [9]; and by the experimental accessibility of metallic TMDCs as single layers [10,11].The realization that CDWs could be different in single layer TMDCs than in analogous bulk materials has drawn attention to the fact that viewing the bulk materials' electronic properties as essentially two-dimensional might be an oversimplification. While reduced dimensionality has a significant impact on electronic instabilities, due to increased electronic correlations and electron-phonon coupling, interlayer coupling also appears to be essential for a full understanding of the electronic properties of these materials [12][13][14][15][16][17]. Specifically, several calculations predict a one-dimensional metallic band formation along the Γ − A direction of the Brillouin zone in the ground state CDW of 1T -TaS 2 (i.e., perpendicular to the planes). This is found in density functional theory calculations [12,16,17], even when electronic correlations are taken into account [14,15]. While the metallic band along Γ−A is universally found in all calculations, the details of the dispersion depend on the stacking order of the CDW unit cell between adjacent planes [15,16]. Angle-resolved photoemission spectroscopy (ARPES)is an experimental technique capable of determining the three-dimensional band structure of crystalline solids, and numerous ARPES studies have been performed on 1T -TaS 2 (for a review see Ref.[2]). However, very little attention has been paid to the possibly three-dimensional ch...

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