12 research outputs found
Pseudodoping of Metallic Two-Dimensional Materials by The Supporting Substrates
We demonstrate how hybridization between a two-dimensional material and its
substrate can lead to an apparent heavy doping, using the example of monolayer
TaS grown on Au(111). Combining calculations, scanning
tunneling spectroscopy experiments and a generic model, we show that strong
changes in Fermi areas can arise with much smaller actual charge transfer. This
mechanism, which we refer to as pseudodoping, is a generic effect for metallic
two-dimensional materials which are either adsorbed to metallic substrates or
embedded in vertical heterostructures. It explains the apparent heavy doping of
TaS on Au(111) observed in photoemission spectroscopy and spectroscopic
signatures in scanning tunneling spectroscopy. Pseudodoping is associated with
non-linear energy-dependent shifts of electronic spectra, which our scanning
tunneling spectroscopy experiments reveal for clean and defective TaS
monolayer on Au(111). The influence of pseudodoping on the formation of charge
ordered, magnetic, or superconducting states is analyzed.Comment: arXiv admin note: substantial text overlap with arXiv:1609.0022
Crystalline and electronic structure of single-layer TaS
Single-layer TaS 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 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.Comment: 6 pages, 4 figure
Quasi-one-dimensional metallic band dispersion in the commensurate charge density wave of
The commensurate charge-density wave (CDW) in the layered compound 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 stacking order of the CDW between adjacent layers, and its periodicity in the c direction is
Quasi-one-dimensional metallic band dispersion in the commensurate charge density wave of 1
Spin-dependent electron-phonon coupling in the valence band of single-layer WS2
The absence of inversion symmetry leads to a strong spin-orbit splitting of the upper valence band of semiconducting single-layer transition-metal dichalchogenides such as MoS2 or WS2. This permits a direct comparison of the electron-phonon coupling strength in states that only differ by their spin. Here, the electron-phonon coupling in the valence band maximum of single-layer WS2 is studied by first-principles calculations and angle-resolved photoemission. The coupling strength is found to be drastically different for the two spin-split branches, with calculated values of lambda(K) = 0.0021 and 0.40 for the upper and lower spin-split valence band of the freestanding layer, respectively. This difference is somewhat reduced when including scattering processes involving the Au(111) substrate present in the experiment but it remains significant, in good agreement with the experimental results
Electron\u2013phonon coupling in single-layer MoS2
The electron\u2013phonon coupling strength in the spin\u2013split valence band maximum of single-layer MoS2 is studied using angle-resolved photoemission spectroscopy and density functional theory-based calculations. Values of the electron\u2013phonon coupling parameter \u3bb are obtained by measuring the linewidth of the spin\u2013split bands as a function of temperature and fitting the data points using a Debye model. The experimental values of \u3bb for the upper and lower spin\u2013split bands at K are found to be 0.05 and 0.32, respectively, in excellent agreement with the calculated values for a free-standing single-layer MoS2. The results are discussed in the context of spin and phase-space restricted scattering channels, as reported earlier for single-layer WS2 on Au(111). The fact that the absolute valence band maximum in single-layer MoS2 at K is almost degenerate with the local valence band maximum at \u393 can potentially be used to tune the strength of the electron\u2013phonon interaction in this material