Search results for "Phonon"

Interaction of two-level systems in amorphous materials with arbitrary phonon fields

2006

To describe the interaction of the two level systems (TLSs) of an amorphous solid with arbitrary strain fields, we introduce a generalization of the standard interaction Hamiltonian. In this new model, the interaction strength depends on the orientation of the TLS with respect to the strain field through a $6\times 6$ symmetric tensor of deformation potential parameters, $[R]$. Taking into account the isotropy of the amorphous solid, we deduce that $[R]$ has only two independent parameters. We show how these two parameters can be calculated from experimental data and we prove that for any amorphous bulk material the average coupling of TLSs with longitudinal phonons is always stronger than …

Jahn-Teller effect in the phonon properties of defective SrTiO3from first principles

2012

the Jahn–Teller effect occurs, thus reducing the cubic symmetry of a perfect crystal and leading to the appearance of both Raman- and infrared-active vibrational modes. The calculated phonon densities of states and group-theoretical analysis of defect-induced phonon frequencies were used for the interpretation of the relevant experimental data, once defect-induced local modes are identified. The temperature dependence of the Vo formation energy based on the calculated Gibbs free energy was also compared with experiments, and the phonon contribution therein estimated.

On time-resolved approach for phonon assisted interband transitions

2015

Photoexcited dynamics of electrons and holes in two-band dielectric, with special emphasis on back reaction of phonons are developed by combining the quantum electrodynamics and Baker-Campbell-Hausdorff (BCH) canonical transformation. These methods create an explicit time-domain representation of photoinduced processes and contribute in unifying phonon-assisted description of distribution functions of electron and hole quasiparticles for the description of observable effects of photoinduced processes in dielectrics.

First-principles LCAO study of phonons in NiWO4

2011

Abstract The electronic, structural and phonon properties of antiferromagnetic wolframite-type NiWO4 have been studied using first-principles spin-polarized LCAO calculations based on the hybrid Hartree-Fock (HF)/density functional (DFT) scheme. The influence of different percentages of HF contribution, i.e. different correlation strength, on the structure and phonon frequencies has been investigated and compared with the available experimental data.

Magnetopolaron in a weakly elliptical InAs/GaAs quantum dot

2003

We study theoretically the properties of a polaron formed in a shallow, weakly elliptical, disk-shaped InAs/GaAs quantum dot in the presence of a magnetic field by using the Davydov's canonical transformation. Special attention is paid to the energy-level splitting due to the Frohlich interaction of an electron in a quantum dot with optical phonons near resonance. The polaron relaxation rates, including the anharmonicity induced channel, are analyzed for various confinement energies and magnetic field magnitudes, taking into account coherent polaronic effects.

One-dimensional quantum-spin—phonon solitons

1983

The quantum dynamics of a compressible harmonic chain of $N$ two-level atoms strongly interacting with the phonons of the lattice is investigated. Two types of mixed excitations are discussed which propagate through the lattice exhibiting solitonic properties. The first type of solitonlike excitation describes the motion of the wall separating two magnetoelastic domains. This transports less energy than the second type of solitonlike excitation which describes the motion of a single spin reversal in the chain. An explicit expression is obtained for the speed of these excitations as a function of an appropriate shape parameter $h$. These results are obtained by approximate self-consistent in…

Phonon Bandwidth and Rate Equations in Avalanche Relaxation

1973

Some comments on fluctuating-elasticity and local oscillator models for anomalous vibrational excitations in glasses

2011

Abstract An overview is given on the present status of the theoretical description of vibrational spectra of glasses, as seen by inelastic neutron, X-ray and light (Raman) scattering. Using the language of Green's/response functions the merits and shortcomings of a local oscillator and a generalized elasticity-theory point of view are discussed. It is pointed out that in both cases the interaction of phonons with disorder-induced irregularities leads to Rayleigh scattering (mean free path l ∝ ω − 4 ) at low enough frequencies and temperatures. In disordered solids at ambient temperature the Rayleigh scattering is usually masqued by Akhiezer-like anharmonic scattering l ∝ ω − 2 , but it can …

Excitonic model for second-order resonant Raman scattering.

1994

A theoretical model for second-order resonant Raman scattering is presented. The effect of Coulomb interaction between electrons and holes is fully taken into account in the framework of the effective-mass approximation. By introducing discrete and continuous excitonic intermediate states in the Raman process, an explicit expression for the Raman scattering efficiency is given for long-range Fr\"ohlich electron-phonon interaction. The model developed can be used to evaluate Raman profiles around the resonant region. A closed-form expression for all matrix elements of the exciton-phonon interaction is obtained once the Coulomb problem for the relative electron-hole motion is separated in sph…

Relaxation and phonons in viscous and glassy orthoterphenyl by neutron scattering

1993

We present an extended set of incoherent neutron scattering measurements on the van der Waals liquido-terphenyl, obtained by time-of-flight and backscattering spectroscopy. In the supercooled liquid regime, data from three instruments are combined and analysed in terms of the selfcorrelationS(Q, t). In the time range 1...100 ps, the crossover from α-to β-relaxation is well described by the masterfunction of mode coupling theory, and fitted parameters are consistent with the previously established critical temperatureT c [Z. Phys. B83, 175 (1991)]. In the glassy regime, vibrations are harmonic and can be described by a density of states. Deviations at lowQ are quantitatively explained by a m…