64 research outputs found
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
A machine learning route between band mapping and band structure
The electronic band structure (BS) of solid state materials imprints the
multidimensional and multi-valued functional relations between energy and
momenta of periodically confined electrons. Photoemission spectroscopy is a
powerful tool for its comprehensive characterization. A common task in
photoemission band mapping is to recover the underlying quasiparticle
dispersion, which we call band structure reconstruction. Traditional methods
often focus on specific regions of interests yet require extensive human
oversight. To cope with the growing size and scale of photoemission data, we
develop a generic machine-learning approach leveraging the information within
electronic structure calculations for this task. We demonstrate its capability
by reconstructing all fourteen valence bands of tungsten diselenide and
validate the accuracy on various synthetic data. The reconstruction uncovers
previously inaccessible momentum-space structural information on both global
and local scales in conjunction with theory, while realizing a path towards
integrating band mapping data into materials science databases
Quasi-free-standing single-layer WS2 achieved by intercalation
Large-area and high-quality single-layer transition metal dichalcogenides can
be synthesized by epitaxial growth on single-crystal substrates. An important
advantage of this approach is that the interaction between the single-layer and
the substrate can be strong enough to enforce a single crystalline orientation
of the layer. On the other hand, the same interaction can lead to hybridization
effects, resulting in the deterioration of the single-layer's native
properties. This dilemma can potentially be solved by decoupling the
single-layer from the substrate surface after the growth via intercalation of
atoms or molecules. Here we show that such a decoupling can indeed be achieved
for single-layer WS2 epitaxially grown on Ag(111) by intercalation of Bi atoms.
This process leads to a suppression of the single-layer WS2-Ag substrate
interaction, yielding an electronic band structure reminiscent of free-standing
single-layer WS2
Absence of superconductivity in ultra-thin layers of FeSe synthesized on a topological insulator
The structural and electronic properties of FeSe ultra-thin layers on
BiSe have been investigated with a combination of scanning
tunneling microscopy and spectroscopy and angle-resolved photoemission
spectroscopy. The FeSe multi-layers, which are predominantly 3-5 monolayers
(ML) thick, exhibit a hole pocket-like electron band at \bar{\Gamma} and a
dumbbell-like feature at \bar{M}, similar to multi-layers of FeSe on
SrTiO. Moreover, the topological state of the Bi2Se3 is preserved beneath
the FeSe layer, as indicated by a heavily \it{n}-doped Dirac cone. Low
temperature STS does not exhibit a superconducting gap for any investigated
thickness down to a temperature of 5 K
An efficient low-density grating setup for monochromatization of XUV ultrafast light sources
Ultrafast light sources have become an indispensable tool to access and understand transient phenomenon in material science. However, a simple and easy-to-implement method for harmonic selection, with high transmission efficiency and pulse duration conservation, is still a challenge. Here we showcase and compare two approaches for selecting the desired harmonic from a high harmonic generation source while achieving the above goals. The first approach is the combination of extreme ultraviolet spherical mirrors with transmission filters and the second approach uses a normal-incidence spherical grating. Both solutions target time- and angle-resolved photoemission spectroscopy with photon energies in the 10-20 eV range but are relevant for other experimental techniques as well. The two approaches for harmonic selection are characterized in terms of focusing quality, efficiency, and temporal broadening. It is demonstrated that a focusing grating is able to provide much higher transmission as compared to the mirror+filter approach (3.3 times higher for 10.8 eV and 12.9 times higher for 18.1 eV), with only a slight temporal broadening (6.8% increase) and a somewhat larger spot size (∼30% increase). Overall, our study establishes an experimental perspective on the trade-off between a single grating normal incidence monochromator design and the use of filters. As such, it provides a basis for selecting the most appropriate approach in various fields where an easy-to-implement harmonic selection from high harmonic generation is needed
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