154 research outputs found
Elementary structural building blocks encountered in silicon surface reconstructions
Driven by the reduction of dangling bonds and the minimization of surface
stress, reconstruction of silicon surfaces leads to a striking diversity of
outcomes. Despite this variety even very elaborate structures are generally
comprised of a small number of structural building blocks. We here identify
important elementary building blocks and discuss their integration into the
structural models as well as their impact on the electronic structure of the
surface
Spontaneous exciton condensation in 1T-TiSe2: a BCS-like approach
Recently strong evidence has been found in favor of a BCS-like condensation
of excitons in 1\textit{T}-TiSe. Theoretical photoemission intensity maps
have been generated by the spectral function calculated within the excitonic
condensate phase model and set against experimental angle-resolved
photoemission spectroscopy data. Here, the calculations in the framework of
this model are presented in detail. They represent an extension of the original
excitonic insulator phase model of J\'erome \textit{et al.} [Phys. Rev. {\bf
158}, 462 (1967)] to three dimensional and anisotropic band dispersions. A
detailed analysis of its properties and further comparison with experiment are
also discussedComment: Submitted to PRB, 11 pages, 7 figure
Superstructure-induced splitting of Dirac cones in silicene
Atomic scale engineering of two-dimensional materials could create devices
with rich physical and chemical properties. External periodic potentials can
enable the manipulation of the electronic band structures of materials. A
prototypical system is 3x3-silicene/Ag(111), which has substrate-induced
periodic modulations. Recent angle-resolved photoemission spectroscopy
measurements revealed six Dirac cone pairs at the Brillouin zone boundary of
Ag(111), but their origin remains unclear [Proc. Natl. Acad. Sci. USA 113,
14656 (2016)]. We used linear dichroism angle-resolved photoemission
spectroscopy, the tight-binding model, and first-principles calculations to
reveal that these Dirac cones mainly derive from the original cones at the K
(K') points of free-standing silicene. The Dirac cones of free-standing
silicene are split by external periodic potentials that originate from the
substrate-overlayer interaction. Our results not only confirm the origin of the
Dirac cones in the 3x3-silicene/Ag(111) system, but also provide a powerful
route to manipulate the electronic structures of two-dimensional materials.Comment: 6 pages, 3 figure
Temperature dependent photoemission on 1T-TiSe2: Interpretation within the exciton condensate phase model
The charge density wave phase transition of 1T-TiSe2 is studied by
angle-resolved photoemission over a wide temperature range. An important
chemical potential shift which strongly evolves with temperature is evidenced.
In the framework of the exciton condensate phase, the detailed temperature
dependence of the associated order parameter is extracted. Having a
mean-field-like behaviour at low temperature, it exhibits a non-zero value
above the transition, interpreted as the signature of strong excitonic
fluctuations, reminiscent of the pseudo-gap phase of high temperature
superconductors. Integrated intensity around the Fermi level is found to
display a trend similar to the measured resistivity and is discussed within the
model.Comment: 8 pages, 6 figure
Applications for ultimate spatial resolution in LASER based -ARPES: A FeSe case study
Combining Angle resolved photoelectron spectroscopy (ARPES) and a
-focused Laser, we have performed scanning ARPES microscopy measurements
of the domain population within the nematic phase of FeSe single crystals. We
are able to demonstrate a variation of the domain population density on a scale
of a few 10 m while constraining the upper limit of the single domain size
to less than 5 . This experiment serves as a demonstration of how
combining the advantages of high resolution Laser ARPES and an ultimate control
over the spatial dimension can improve investigations of materials by reducing
the cross contamination of spectral features of different domains
Detection of decoupled surface and bulk states in epitaxial orthorhombic SrIrO3 thin films
We report the experimental evidence of evolving lattice distortion in high quality epitaxial orthorhombic SrIrO3(001) thin films fully strained on (001) SrTiO3 substrates. Angle-resolved X-ray photoemission spectroscopy studies show that the surface layer of 5 nm SrIrO3 films is Sr–O terminated, and subsequent layers recover the semimetallic state, with the band structure consistent with an orthorhombic SrIrO3(001) having the lattice constant of the substrate. While there is no band folding in the experimental band structure, additional super-periodicity is evident in low energy electron diffraction measurements, suggesting the emergence of a transition layer with crystal symmetry evolving from the SrTiO3 substrate to the SrIrO3(001) surface. Our study sheds light on the misfit relaxation mechanism in epitaxial SrIrO3 thin films in the orthorhombic phase, which is metastable in bulk
An Alternative Interpretation of Recent ARPES Measurements on TiSe2
Recently there has been a renewed interest in the charge density wave
transition of TiSe2, fuelled by the possibility that this transition may be
driven by the formation of an excitonic insulator or even an excitonic
condensate. We show here that the recent ARPES measurements on TiSe2 can also
be interpreted in terms of an alternative scenario, in which the transition is
due to a combination of Jahn-Teller effects and exciton formation. The hybrid
exciton-phonons which cause the CDW formation interpolate between a purely
structural and a purely electronic type of transition. Above the transition
temperature, the electron-phonon coupling becomes ineffective but a finite
mean-field density of excitons remains and gives rise to the observed diffuse
ARPES signals.Comment: 4 pages, 2 figure
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