Search results for "density of state"
showing 10 items of 187 documents
Quantum simulation of the spin-boson model with a microwave circuit
2017
We consider superconducting circuits for the purpose of simulating the spin-boson model. The spin-boson model consists of a single two-level system coupled to bosonic modes. In most cases, the model is considered in a limit where the bosonic modes are sufficiently dense to form a continuous spectral bath. A very well known case is the ohmic bath, where the density of states grows linearly with the frequency. In the limit of weak coupling or large temperature, this problem can be solved numerically. If the coupling is strong, the bosonic modes can become sufficiently excited to make a classical simulation impossible. Here, we discuss how a quantum simulation of this problem can be performed …
Plasmon polaritons of metallic nanowires for controlling submicron propagation of light
1999
Laboratoire de Physique, Optique Submicronique, Universite´de Bourgogne, BP 47870, F-21078 Dijon, France~Received 29 April 1999!We use the Green dyadic technique to study the propagation of a local excitation along metallic nanowiresof a subwavelength cross section. The metallic nanowires are elongated parallelepipeds deposited on a trans-parent substrate. A tightly focused plane wave illuminates one end of the nanowires. The localized surface-plasmon resonances of the nanowires propagate the local excitations over distances larger than the incidentwavelength. The properties of the electromagnetic eigenmodes of the nanowires are analyzed in terms of thelocal density of states. @S0163-1829~9…
Gilbert damping of CoFe-alloys
2019
We report structural, magnetic and dynamic properties of polycrystalline Coalt;subagt;xalt;/subagt;Fealt;subagt;1-xalt;/subagt;-alloy films on Sapphire, Silicon and MgO substrates across the full composition range, by using a Vector Network Analyser ferromagnetic resonance measurement technique (VNA-FMR), Superconducting Quantum Interference Device magnetometry (SQUID) and X-Ray Diffraction (XRD). In the approximate vicinity of 28% Co, we observe a minimum of the damping parameter, associated with a reduction in the density of states to a minimum value at the Fermi energy level. For films on all substrates, we find magnetic damping of the order of 4-5⋅10alt;supagt;-3alt;/supagt;, showing th…
(Invited) The Effect of (La,Sr)MnO 3 Cathode Surface Termination on Its Electronic Structure
2017
La1-xSrxMnO3 (LSM) was one of the first perovskites used as SOFC cathode material. Its (001) surface has two possible terminations, LaSrO and MnO2, with quite different properties and oxygen reduction efficiencies. To avoid effects of surface polarity and the dipole moment across the material, symmetric non-stoichiometric slabs are commonly used in theoretical calculations with identical terminating planes on its both sides. We analyzed the dependence of the electronic structure (density of states) and charge distribution (effective atomic charges and chemical bond covalency) on the slab termination and Mn ion oxidation state (controlled by the Sr content and slab nonstoichiometry).
Dopant Clusterization and Oxygen Coordination in Ta-Doped Bismuth Oxide: A Structural and Computational Insight into the Mechanism of Anion Conduction
2015
Bi2O3 in its fluorite-like form can be obtained either at 730-824 °C, showing the highest oxide-ion conduction known so far, or by doping. We present a comprehensive appraisal of the local atomic structure of Ta-doped Bi2O3 investigating by X-ray absorption spectroscopy the aggregation motifs of Ta5+ and the interaction between dopants and oxygen vacancies. Using periodic density functional theory simulations, we show that the connection of Ta4O18 aggregates is energetically favorable. We find that the local coordination of Bi3+ and its electronic structure, as seen from the calculated density of states (DOS), are invariably determined by the Bi 6s2 lone pair in both doped and undoped Bi2O3…
Evidence of superatom electronic shells in ligand-stabilized aluminum clusters
2011
Ligand-stabilized aluminum clusters are investigated by density functional theory calculations. Analysis of Kohn-Sham molecular orbitals and projected density of states uncovers an electronic shell structure that adheres to the superatom complex model for ligand-stabilized aluminum clusters. In this current study, we explain how the superatom complex electron-counting rule is influenced by the electron-withdrawing ligand and a dopant atom in the metallic core. The results may guide the prediction of new stable ligand-stabilized (superatom) complexes, regardless of core and electron-withdrawing ligand composition.
Harmonic behavior of trehalose-coated carbon-monoxy-myoglobin at high temperature.
1999
Abstract Embedding biostructures in saccharide glasses protects them against extreme dehydration and/or exposure to very high temperature. Among the saccharides, trehalose appears to be the most effective bioprotectant. In this paper we report on the low-frequency dynamics of carbon monoxy myoglobin in an extremely dry trehalose glass measured by neutron spectroscopy. Under these conditions, the mean square displacements and the density of state function are those of a harmonic solid, up to room temperature, in contrast to D 2 O-hydrated myoglobin, in which a dynamical transition to a nonharmonic regime has been observed at ∼180K (Doster et al., 1989. Nature. 337:754–756). The protective ef…
Temperature and doping dependence of normal state spectral properties in a two-orbital model for ferropnictides
2016
Using a second-order perturbative Green's functions approach we determined the normal state single-particle spectral function $A(\vec{k},\omega)$ employing a minimal effective model for iron-based superconductors. The microscopic model, used before to study magnetic fluctuations and superconducting properties, includes the two effective tight-binding bands proposed by S.Raghu et al. [Phys. Rev. B 77, 220503 (R) (2008)], and intra- and inter-orbital local electronic correlations, related to the Fe-3d orbitals. Here, we focus on the study of normal state electronic properties, in particular the temperature and doping dependence of the total density of states, $A(\omega)$, and of $A(\vec{k},\o…
Enhanced resonant force between two entangled identical atoms in a photonic crystal
2013
We consider the resonant interaction energy and force between two identical atoms, one in an excited state and the other in the ground state, placed inside a photonic crystal. The atoms, having the same orientation of their dipole moment, are supposed prepared in their symmetrical state and interact with the quantum electromagnetic field. We consider two specific models of photonic crystals: a one-dimensional model and an isotropic model. We show that in both cases the resonant interatomic force can be strongly enhanced by the presence of the photonic crystal, as a consequence of the modified dispersion relation and density of states, in particular if the transition frequency of the atoms i…
Simultaneous determination of carrier lifetime and electron density-of-states in P3HT:PCBM organic solar cells under illumination by impedance spectr…
2010
We report new insights into recombination kinetics in poly(3-hexylthiophene):methanofullerene (P3HT:PCBM) bulk heterojunction (BHJ) solar cells, based on simultaneous determination of the density of states (DOS), internal recombination resistance, and carrier lifetime, at different steady states, by impedance spectroscopy. A set of measurements at open circuit under illumination was performed aiming to better understand the limitations to the photovoltage, which in this class of solar cells remains far below the theoretical limit which is the difference between the LUMO level of PCBM and the HOMO of P3HT (∼1.1 eV). Recombination kinetics follows a bimolecular law, being the recombination ti…