Search results for "Band structure"
showing 10 items of 215 documents
First-principles investigation of the bulk and low-index surfaces ofMoSe2
2014
In the framework of density functional theory, the geometry, electronic structure, and magnetic properties of the bulk and low index surfaces of $\mathrm{Mo}{\mathrm{Se}}_{2}$ have been studied. We have carried out calculations with various exchange-correlation functionals to select one which is able to describe the van der Waals (vdW) interactions and gives the best geometry compared with experiments. The inclusion of the vdW forces, however, does not guarantee a reliable description for the geometry of this compound: some vdW functionals strongly overestimate the interlayer distance, similar to GGA functionals. Our investigation shows that the recently introduced optB86b-vdW functional yi…
Spin-layer locking of interlayer excitons trapped in moir\'e potentials
2019
Van der Waals heterostructures offer attractive opportunities to design quantum materials. For instance, transition metal dichalcogenides (TMDs) possess three quantum degrees of freedom: spin, valley index, and layer index. Further, twisted TMD heterobilayers can form moir\'e patterns that modulate the electronic band structure according to atomic registry, leading to spatial confinement of interlayer exciton (IXs). Here we report the observation of spin-layer locking of IXs trapped in moir\'e potentials formed in a heterostructure of bilayer 2H-MoSe$_2$ and monolayer WSe$_2$. The phenomenon of locked electron spin and layer index leads to two quantum-confined IX species with distinct spin-…
Electronic structure calculations forZnFe2O4
2011
Local density approximation was applied to scrutinize the electronic structure and magnetic properties of the spinel ferrite ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$. Various cation distributions were established to obtain the ground state for the system. In magnetic crystals, the position of the atoms is not enough for symmetry determination. A structure prediction by decreasing the octahedral point group symmetry ${\mathrm{O}}_{h}$ of Fe to ${\mathrm{D}}_{4h}$, ${\mathrm{C}}_{4v}$, and ${\mathrm{C}}_{3v}$ was carried out. The effect of the exchange and correlation terms on the band structure of ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$ was studied by the generalized gradient approximation $+$ th…
Electronic structure studies ofBaFe2As2by angle-resolved photoemission spectroscopy
2009
We report high resolution angle-resolved photoemission spectroscopy (ARPES) studies of the electronic structure of ${\text{BaFe}}_{2}{\text{As}}_{2}$, which is one of the parent compounds of the Fe-pnictide superconductors. ARPES measurements have been performed at 20 and 300 K, corresponding to the orthorhombic antiferromagnetic phase and the tetragonal paramagnetic phase, respectively. Photon energies between 30 and 175 eV and polarizations parallel and perpendicular to the scattering plane have been used. Measurements of the Fermi surface yield two hole pockets at the $\ensuremath{\Gamma}$ point and an electron pocket at each of the $X$ points. The topology of the pockets has been conclu…
Optical studies of gap, hopping energies, and the Anderson-Hubbard parameter in the zigzag-chain compoundSrCuO2
2001
We have investigated the electronic structure of the zig-zag ladder (chain) compound ${\mathrm{SrCuO}}_{2}$ combining polarized optical absorption, reflection, photoreflectance, and pseudo-dielectric-function measurements with the model calculations. These measurements yield an energy gap of 1.42 eV (1.77 eV) at 300 K along (perpendicular to) the Cu-O chains. We have found that the lowest-energy gap, the correlation gap, is temperature independent. The electronic structure of this oxide is calculated using both the local-spin-density approximation with gradient correction method and the tight-binding theory for the correlated electrons. The calculated density of electronic states for noncor…
Unraveling exciton dynamics in amorphous silicon dioxide: Interpretation of the optical features from 8 to 11 eV.
2011
Physical review / B 83, 174201 (2011). doi:10.1103/PhysRevB.83.174201
Analysis of broadband x-ray spectra of highly charged krypton from a microcalorimeter detector of an electron-beam ion trap
2001
Spectra of highly charged Kr ions, produced in an electron-beam ion trap (EBIT), have been recorded in a broad x-ray energy band (0.3 keV to 4 keV) with a microcalorimeter detector. Most of the spectral lines have been identified as transitions of B- to Al-like Kr. The transition energies have been determined with 0.2% uncertainty. A semi-empirical EBIT plasma model has been created to calculate a synthetic spectrum of highly charged Kr and to determine a charge state distribution of Kr ions inside the EBIT.
Sub-Diffractive Band-Edge Solitons in Bose-Einstein Condensates in Periodic Potentials
2006
A new type of matter wave diffraction management is presented that leads to sub-diffractive soliton-like structures. The proposed management technique uses two counter-moving, identical periodic potentials (e.g. optical lattices). For suitable lattice parameters a novel type of atomic band-gap structure appears in which the effective atomic mass becomes infinite at the lowest edge of an energy band. This way normal matter-wave diffraction (proportional to the square of the atomic momentum) is replaced by fourth-order diffraction, and hence the evolution of the system becomes sub-diffractive.
Crystal symmetry and pressure effects on the valence band structure ofγ-InSe andε-GaSe: Transport measurements and electronic structure calculations
2005
This paper reports on Hall effect and resistivity measurements under high pressure up to 3--4 GPa in $p$-type $\ensuremath{\gamma}$-indium selenide (InSe) (doped with As, Cd, or Zn) and $\ensuremath{\epsilon}$-gallium selenide (GaSe) (doped with N or Sn). The pressure behavior of the hole concentration and mobility exhibits dramatic differences between the two layered compounds. While the hole concentration and mobility increase moderately and monotonously in $\ensuremath{\epsilon}$-GaSe, a large increase of the hole concentration near 0.8 GPa and a large continuous increase of the hole mobility, which doubled its ambient pressure value by 3.2 GPa, is observed in $\ensuremath{\gamma}$-InSe.…
Notice of Removal: Stochastic generation of the phononic band structure of lossy and infinite crystals
2017
The concept of the band structure is central to the field of phononic crystals. Indeed, capturing the dispersion of Bloch waves — the eigenmodes of propagation in periodic media — gives invaluable information on allowed propagation modes, their phase and group velocities, local resonances, and band gaps. Band structures are usually obtained by solving an eigenvalue problem defined on a closed and bounded domain, which results in a discrete spectrum. There are at least two cases, however, that cannot be reduced to a simple eigenvalue problem: first, when materials showing dispersive loss are present and second, when the unit-cell extends beyond any bound, as in the case of phononic crystal o…