Search results for "Band structure"
showing 10 items of 215 documents
Structure of rotational bands in 253No
2009
In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the 253 No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the $\ensuremath 9/2^-[734]_{\nu}$ ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work.
Intravalley spin-flip relaxation dynamics in single-layer WS2
2019
Two-dimensional Transition Metal Dichalcogenides (TMDs) have been widely studied because of the peculiar electronic band structure and the strong excitonic effects [1]. In these materials the large spin-orbit coupling lifts the spin degeneracy of the valence (VB) and the conduction band (CB) giving rise to the A and B interband excitonic transitions. In monolayer WS2, the spins of electrons in the lowest CB and in the highest VB at K/K' point of the Brillouin zone are antiparallel resulting in an intravalley dark exciton state at a lower energy than the bright exciton, see left panel of Fig.1. On the one hand, the presence of dark excitons has been revealed indirectly from the observation o…
Metal valence states inEu0.7NbO3,EuNbO3,andEu2Nb5O9by TB-LMTO-ASA band-structure calculations and resonant photoemission spectroscopy
1998
The electronic structures of ${\mathrm{Eu}}_{2}{\mathrm{Nb}}_{5}{\mathrm{O}}_{9},$ ${\mathrm{EuNbO}}_{3},$ and ${\mathrm{Eu}}_{0.7}{\mathrm{NbO}}_{3}$ have been investigated by photoemission and total-yield spectroscopy with synchrotron radiation, and in the case of ${\mathrm{Eu}}_{2}{\mathrm{Nb}}_{5}{\mathrm{O}}_{9}$ by tight-binding linear muffin-tin orbital (LMTO) band-structure calculations. A central question for reduced europium niobates is that of the valence of Eu and Nb. Both europium and niobium atoms can appear in different valence states so that various electronic configurations in the title compounds are possible. For this reason, the valence band was studied by the resonant Eu…
THE LIMITING EFFICIENCY OF FOUR-BAND CELLS REVISITED
2014
The limiting theoretical efficiency of four-band solar cells is revisited. In previous work, researchers have looked at the theoretical efficiency of four band cells where the smallest of the three sub-band gaps is closest to the valence band and the largest closest to the conduction band. In this work, limits are calculated also for other possible band configurations. In multi-band cells, photon selectivity can be assured by adjusting the band widths. The present work shows that previous authors have put too rigid constraints on the band structure to achieve spectral selectivity. Relieving these constraints gives a considerably higher limiting efficiency for cells with band width restricti…
Photon bunching of the nonlinear photoluminescence emitted by plasmonics metals
2021
International audience; In this report, we investigate the statistical temporal distribution of nonlinear upconverted photoluminescence emitted by gold and silver nanostructures excited by focused near-infrared laser pulses. We systematically observe a clear signature of photon bunching regardless of the nano-object's geometry, material's crystalline arrangement, and electronic band structure. The similarity of the data obtained across very different plasmonic objects confirms that these types of nonlinear radiation share a common chaotic origin and result from a collection of emitters. The correlation of photons at a picosecond time scale released by nanoscale nonlinear sources of broadban…
A Preliminary BeppoSAX Study of the (Bright) Atoll Source GX 9+1
2003
We report the preliminary results of a 350 ks BeppoSAX observation of the bright atoll source GX 9+1. In the field of view of the MECS instrument we discovered a X-ray pulsar, designated SAX J1802.7 - 2017, at an angular distance from GX 9+1 of ∼ 22 ′ . Since the X-ray emission of SAX J1802.7 - 2017 contaminates the energy spectrum above 10 keV we studied the energy spectrum of GX 9+1 in the energy band 0.1 - 10keV. We selected four regions in the color-color diagram and extracted one spectrum from each region. A bump below 1keV is present in the spectra using a model composed by a Comptonized component absorbed by neutral matter having an equivalent hydrogen column of 1.5 x 10 22 cm -2 . T…
Rich band structure and multiple long-lived isomers in the odd-odd Cs118 nucleus
2021
Level-spacing distribution in the tight-binding model of fcc clusters.
1993
A lattice-gas Monte Carlo method is used to simulate metallic fcc clusters at finite temperatures. A tight-binding model including s and p electrons has been derived for reproducing the free-electron-like energy band for the bulk metal and this model is used for calculating the electronic structures of the fcc cluster. The resulting level-spacing distribution at the Fermi energy is a Wigner distribution. The width of the distribution in small clusters is smaller than that calculated from the bulk density of states. In the lattice gas clusters the energy gaps related to the electronic magic numbers do not show up at the Fermi level. The energy between the last occupied and the first unoccupi…
Valence bands of poly(methylmethacrylate) and photoion emission in vacuum ultraviolet region
1992
Photoion and photoelectron yields were measured for poly(methylmethacrylate) in the photon energy region of 8–40 eV using synchrotron radiation. Further, the valence‐band structure was investigated with ultraviolet photoelectron spectra and valence effective Hamiltonian calculations. A significant difference was observed between the photon energy dependencies of photoion and photoelectron yields. The threshold energy for photoion emission was found to be 10.5 eV, while that for photoelectron emission was 8.5 eV, indicating holes created near the valence‐band top do not contribute to the ion emission. At the higher‐energy region, the ion emission efficiency was found to be enhanced in the ph…
A New Approach to Deriving Interatomic Many-Body Interactions in Metals
1998
An original method of treating the kinetic and exchange-correlation en- ergies functionals in terms of many particle interactions was developed. It is based on utilizing the local density approximation. The total electron density, extracted from the ab initio . band structure calculations, is expressed as a lin- ear superposition of contributions from the individual pseudoions embedded in the uniform background. The explicit expressions for the pair and triplet potentials are presented. The general form for the part of the pair interatomic interactions caused by the kinetic and. the exchange-correlation effects is ob- tained. Relationship between the developing approach and the perturbation…