Light scattering observations of spin reversal excitations in the fractional quantum Hall regime

Resonant inelastic light scattering experiments access the low lying excitations of electron liquids in the fractional quantum Hall regime in the range 2/5≥ν≥1/3. Modes associated with changes in the charge and spin degrees of freedom are measured. Spectra of spin reversed excitations at filling factor ν?1/3 and at ν?2/5 identify a structure of lowest spin-split Landau levels of composite fermions (CFs) that is similar to that of electrons. Observations of spin wave excitations enable determinations of energies required to reverse spin. The spin reversal energies obtained from the spectra illustrate the significant residual interactions of composite fermions. At ν=1/3 energies of spin reversal modes are larger but relatively close to spin conserving excitations that are linked to activated transport. Predictions of composite fermion theory are in good quantitative agreement with experimental results.     

Light scattering from non-equilibrium electron excitations in semiconductors

Light scattering from non equilibrium single-particle electron excitations in direct gap n-doped semiconductors is considered. It is shown that, in quasi-equilibrium conditions, deviations from the Maxwellian profile of the scattering spectrum of hot electrons can be accounted for by exchange and correlation effects.     

Light scattering lineshape in opaque materials

The wavevector distribution excited by light scattering in opaque materials is calculated and compared to recently observed asymmetrical Brillouin lineshapes.     

Light scattering from spin waves in superfluid3He-A

Summary We show that in theA-phase of superfluid³He one may expect the Mandelstam-Brillouin light scattering from spin waves. The scattering is caused by fluctuations of the magnetic susceptibility.

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Riassunto Si mostra che nella faseA del superfluido³He ci si può aspettare diffusione di luce di Mandelstam-Brillouin da onde di spin. La diffusione è caratterizzata da fluttuazioni della suscettibilità magnetica.

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Резюме Мы покаем, что ьА-qfазе сьерхтекучего³He μожно ожидать рассеяние света Мандельштама-Бриллюэна на спиновых волнах. Рассеяние обусповлено флуктациями магнитной восприимчивости.

     

Localized spin excitations in magnets with triangular spin ordering

Some types of localized spin excitations in hexagonal antiferromagnets with triangular spin ordering are investigated. The character of relaxation of these spin excitations is studied.     

Nature of spin excitations in two-dimensional mott insulators: undoped cuprates and other materials

We investigate the excitation spectrum of a two-dimensional resonating valence bond (RVB) state. Treating the pi-flux phase with antiferromagnetic correlations as a variational ground state, we recover the long wavelength magnon as an "RVB exciton." However, this excitation does not exhaust the entire spectral weight and the high-energy spectrum is dominated by fermionic excitations. The latter can be observed directly by inelastic neutron scattering, and we predict their characteristic energy scales along different high symmetry directions in the magnetic Brillouin zone. We also interpret experimental results on two magnon Raman scattering and midinfrared absorption within this scenario.     

Low energy excitations in spin glasses

We discuss the nature of excitations that govern the low temperature thermodynamic behaviour of spin glasses and propose that the spin glass state is a space-time dependent ground state of a system of interacting spins wherein rotational invariance is broken spontaneously.     

Two-electron excitations in helium-like ions by inelastic photon scattering

Inelastic photon scattering by helium atoms and helium-like ions with simultaneous excitation of the two-electron transition 1s ²→2s ² is examined in the nonrelativistic energy range I≪ω≪m (I is the ionization potential, ω is the photon energy, m is the electron mass, and ℏ=c=1). The electrons are assumed to be moving in the Coulomb field of the nucleus, and the electron-electron interaction is taken into account in the lowest perturbation order. The differential and total cross sections of the process and the autoionization width of the 2s ² energy level are calculated. The numerical value of the autoionization width is found to agree with the results of the more rigorous calculations of other researchers. Zh. éksp. Teor. Fiz. 113, 539–549 (February 1998)     

Muon spin relaxation by electronic excitations moving in one dimension

The manner in which an electronic spin, executing a linear random walk, e.g. along a polymer chain, depolarizes a muon (or proton) probe spin, is investigated by computer simulation. The essential features of the model are the assumptions of a contact hyperfine interaction with limited range and of loss of coherence between successive encounters. The low dimensionality of the motion is reflected in the shape of the relaxation functions generated, which depart significantly from simple exponentials. Fits to various functional forms are examined for different combinations of hop rate and chain length, hyperfine constant and applied magnetic field. This revised version was published online in August 2006 with corrections to the Cover Date.     

Raman scattering by electron and phonon excitations in FeSi

The temperature evolution of Raman scattering by electron and phonon excitations in FeSi is studied within the range of 10–500 K. At low temperatures, the frequency dependence for the spectra of light scattered by electrons exhibits vanishing intensity in the range up to 500–600 cm^–1, which suggests the existence of an energy gap of about 70 meV. The calculations of the electronic excitation spectra based on the band structure determined using the LDA+DMFT technique (local electron density + dynamic mean field approximation) are in good agreement with the low-temperature experimental data and confirm that FeSi is a material with intermediate electron correlations. The changes in the shape of the electronic excitation spectrum and in the self-energy of optical phonons indicate a transition to the metallic state above 100 K. The analysis of experimental data demonstrates an appreciable decrease in the electron lifetime with the growth of temperature determining the (insulator–poor metal) transition.     

Rotational excitations in muonic atom scattering by molecular hydrogen

A computational scheme based on the infinite order sudden approximation (IOS) is proposed for treating molecular and screening effects in muonic atom scattering at low energies. With this scheme the differential (dσ/dΩ(ɛj← 0|θ) and the total σ_tot(ɛ) cross-sections of muonic atom scattering on molecules of hydrogen isotopes are calculated at energies ɛ_rot=ℏω_I⩽ɛ⩽ɛ_vib= ℏω_03BD;. The IOS permits a quantitative analysis of the dependence of the differential cross-sections on the scattering angle and on the rotational excitations, particularly the rotational rainbow effects. An attractive feature of this approach is also to include the energy and the angular dependencies in the “input” cross-sections describing the muonic atom scattering on each bare nucleus of the molecule. The calculated total cross-sections ω_tot(ɛ) are in agreement with the data obtained earlier with the pseudopotential approach. This revised version was published online in August 2006 with corrections to the Cover Date.     

Light scattering by fluffy particles with the PROGRA experiment: Mixtures of materials

The PROGRA² experiment is specifically designed to measure the linear polarization of the light scattered by clouds of particles. The imaging method allows us to obtain maps of polarization and to measure the size distribution and the number density of the particles in the field of view. This work presents a systematic study of highly porous (fluffy) aggregates with submicron-sized constituent grains lifted by an air-draught. The main materials are silica and carbon. The maximum in polarization mainly depends on the average size of the constituent grains. The results, mainly concerned with the negative branch of the phase curves, the maximum polarization, the color effect and the albedo are compared with cometary observations and discussed in terms of physical properties.     

Longitudinal magnetic excitations in classical spin systems

Using spin dynamics simulations we predict the splitting of the longitudinal spin-wave peak in all antiferromagnets with single site anisotropy into two peaks separated by twice the energy gap at the Brillouin zone center. This phenomenon has yet to be observed experimentally but can be easily investigated through neutron scattering experiments on MnF2 and FeF2. We have also determined that for all classical Heisenberg models the longitudinal propagative excitations are entirely multiple spin wave in nature.     

Elementary spin excitations in ultrathin itinerant magnets

Elementary spin excitations (magnons) play a fundamental role in condensed matter physics, since many phenomena e.g. magnetic ordering, electrical (as well as heat) transport properties, ultrafast magnetization processes, and most importantly electron/spin dynamics can only be understood when these quasi-particles are taken into consideration. In addition to their fundamental importance, magnons may also be used for information processing in modern spintronics.     

Magnetic excitations in sinusoidally modulated spin structures

We show by using a simple model that in incommensurate sinusoidally modulated spin structures, such as those found in Er and Tm just below their magnetic ordering temperatures and in the ordered phase of Cr, the magnon modes are broadened due to the spatial fluctuations of the exchange and anisotropy energies.     

d-d excitations in manganites probed by resonant inelastic x-ray scattering

We report a study of electronic excitations in manganites exhibiting a range of ground states, using resonant inelastic x-ray scattering (RIXS) at the Mn K edge. Excitations with temperature dependent changes correlated with the magnetism were observed as high as 10 eV. By calculating Wannier functions, and finite-q response functions, we associate this dependence with intersite d-d excitations. The calculated dynamical structure factor is found to be similar to the RIXS spectra.     

Nuclear effective interactions and spin excitations

In view of the one-boson-exchange model for the nucleon-nucleon interaction and the Hartree-Fock (HF) interaction, we formulate the effective interactions for particle-hole states in terms of the exchange of the fields which are confined in the nucleus. This theory, as an extension to the nuclear field theory (NFT), takes into account the propagation of the fields which is neglected in NFT. The effective interactions thus obtained reproduce the energies of a sequence of electric giant resonances and the core polarizabilities associated with the resonances. It is found that the coupling constants of the σ- and ω-fields are suppressed for the particle-hole interaction by 60% with respect to the HF interaction. As for the effective interactions involving nucleon spins, we consider the fields coupled to nucleon spins. The effective interactions obtained, essentially different from those in NFT, have a tensor component. We analyse the energies and cross sections for excitation of stretched spin particle-hole states which are the most sensitive to the tensor force. The effective interaction responsible for the stretched spin states is shown to be consistent with that for the magnetic resonances observed in the (p, n) reactions.