100 research outputs found
Impact of electron-hole correlations on the electronic structure
Several experiments have been performed on 1T−TiSe2 in order to identify whether the electronic structure is semimetallic or semiconducting without reaching a consensus. In this Letter, we theoretically study the impact of electron-hole and electron-phonon correlations on the bare semimetallic and semiconducting electronic structure. The resulting electron spectral functions provide a direct comparison of both cases and demonstrate that 1T−TiSe2 is of predominant semiconducting character with some spectral weight crossing the Fermi level
Limited genetic diversity and high differentiation among the remnant adder ( Viperaberus ) populations in the Swiss and French Jura Mountains
Although the adder (Viperaberus) has a large distribution area, this species is particularly threatened in Western Europe due to high habitat fragmentation and human persecution. We developed 13 new microsatellite markers in order to evaluate population structure and genetic diversity in the Swiss and French Jura Mountains, where the species is limited to only a few scattered populations. We found that V.berus exhibits a considerable genetic differentiation among populations (global FST=0.269), even if these are not geographically isolated. Moreover, the genetic diversity within populations in the Jura Mountains and in the less perturbed Swiss Alps is significantly lower than in other French populations, possibly due to post-glacial recolonisation processes. Finally, in order to minimize losses of genetic diversities within isolated populations, suggestions for the conservation of this species in fragmented habitats are propose
Exciton Condensation Driving the Periodic Lattice Distortion of 1T-TiSe₂
We address the lattice deformation of 1T-TiSe₂ within the exciton condensate phase. We show that, at low temperature, condensed excitons influence the lattice through electron-phonon interaction. It is found that at zero temperature, in the exciton condensate phase of 1T-TiSe₂, this exciton condensate exerts a force on the lattice generating ionic displacements comparable in amplitude to what is measured in experiment. This is thus the first quantitative estimation of the amplitude of the periodic lattice distortion observed in 1T-TiSe₂ as a consequence of the exciton condensate phase
Inhibition of the photoinduced structural phase transition in the excitonic insulator TaNiSe
Femtosecond time-resolved mid-infrared reflectivity is used to investigate
the electron and phonon dynamics occurring at the direct band gap of the
excitonic insulator TaNiSe below the critical temperature of its
structural phase transition. We find that the phonon dynamics show a strong
coupling to the excitation of free carriers at the \Gamma\ point of the
Brillouin zone. The optical response saturates at a critical excitation fluence
~mJ/cm due to optical absorption saturation. This
limits the optical excitation density in TaNiSe so that the system
cannot be pumped sufficiently strongly to undergo the structural change to the
high-temperature phase. We thereby demonstrate that TaNiSe exhibits a
blocking mechanism when pumped in the near-infrared regime, preventing a
nonthermal structural phase transition
Ultrafast Electronic Band Gap Control in an Excitonic Insulator
We report on the nonequilibrium dynamics of the electronic structure of the
layered semiconductor TaNiSe investigated by time- and angle-resolved
photoelectron spectroscopy. We show that below the critical excitation density
of mJ cm, the band gap transiently, while it is
above . Hartree-Fock calculations reveal that this effect can
be explained by the presence of the low-temperature excitonic insulator phase
of TaNiSe, whose order parameter is connected to the gap size. This
work demonstrates the ability to manipulate the band gap of TaNiSe with
light on the femtosecond time scale
A new structural model for the Si(331)-(12x1) reconstruction
A new structural model for the Si(331)-(12x1) reconstruction is proposed.
Based on scanning tunneling microscopy images of unprecedented resolution,
low-energy electron diffraction data, and first-principles total-energy
calculations, we demonstrate that the reconstructed Si(331) surface shares the
same elementary building blocks as the Si(110)-(16x2) surface, establishing the
pentamer as a universal building block for complex silicon surface
reconstructions
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
Quasi one-dimensional Ag nanostructures on Si(331)–(12 × 1)
We report on the deposition of sub-monolayer Ag on the Si(331)–(12 × 1) surface. The growth of one-dimensional Ag nanostructures is observed by means of low- temperature scanning tunneling microscopy and low energy electron diffraction. We find that the deposited Ag is organized in nanostructures consistently taking “sawtooth” shapes. While the structures are not perfectly organized, their back edges are atomically straight. The limitations of this system in terms of faceting are also discussed
Orbital breathing effects in the computation of x-ray d-ion spectra in solids by ab initio wave-function-based methods
In existing theoretical approaches to core-level excitations of
transition-metal ions in solids relaxation and polarization effects due to the
inner core hole are often ignored or described phenomenologically. Here we set
up an ab initio computational scheme that explicitly accounts for such physics
in the calculation of x-ray absorption and resonant inelastic x-ray scattering
spectra. Good agreement is found with experimental transition-metal -edge
data for the strongly correlated cuprate LiCuO, for which we
determine the absolute scattering intensities. The newly developed methodology
opens the way for the investigation of even more complex electronic
structures of group VI B to VIII B correlated oxide compounds
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