Effect of electron-phonon interaction on the shift and attenuation of optical phonons

Using the Boltzmann equation for electrons in metals, we show that the optical phonons soften and have a dispersion due to screening in agreement with the results reported recently [M. Reizer, Phys. Rev. B {\bf 61}, 40 (2000)]. Additional phonon damping and frequency shift arise when the electron--phonon interaction is properly included.Comment: 4 pages, late

Electronic Raman scattering and photoluminescence from La0.7_{0.7}Sr0.3_{0.3}MnO3_3 exhibiting giant magnetoresistance

Raman and Photoluminescence (PL) experiments on correlated metallic La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ have been carried out using different excitation wavelengths as a function of temperature from 15 K to 300 K. Our data suggest a Raman mode centered at 1800 cm$^{-1}$ and a PL band at 2.2 eV. The intensities of the two peaks decrease with increasing temperature. The Raman mode can be attributed to a plasmon excitation whose frequency and linewidths are consistent with the measured resistivities. The PL involves intersite electronic transitions of the manganese ions.Comment: 10 pages + 4 eps figures, Revtex 3.0, figures available on reques

Raman scattering by the lattice of ionic crystals containing impurities

Theory of the impurity-induced Raman scattering in crystals with NaCl structure. It is shown that the first-order Raman effect is not produced by alteration of the mass defect but by change in the force constant.Théorie de la diffusion Raman induite par la présence d'impuretés dans les cristaux du type NaCl. On montre que l'effet Raman du premier ordre n'est pas produit par l'altération de la masse, mais par celle de la constante de force

Persistence of regular motions for nearly integrable Hamiltonian systems in the thermodynamic limit

A review is given of the studies aimed at extending to the thermodynamic limit stability results of Nekhoroshev type for nearly integrable Hamiltonian systems. The physical relevance of such an extension, i. e., of proving the persistence of regular (or ordered) motions in that limit, is also discussed. This is made in connection both with the old Fermi – Pasta – Ulam problem, which gave origin to such discussions, and with the optical spectral lines, the existence of which was recently proven to be possible in classical models, just in virtue of such a persistence

Magnetic polarons and the metal-semiconductor transitions in (

We present inelastic light scattering measurements of EuO and Eu$_{1-x}$La$_{x}$B$_6$ ($x$=0, 0.005, 0.01, 0.03, and 0.05) as functions of doping, B isotope, magnetic field, and temperature. Our results reveal a variety of distinct regimes as a function of decreasing T: (a) a paramagnetic semimetal regime, which is characterized by a collision-dominated electronic scattering response whose scattering rate $\Gamma$ decreases with decreasing temperature; (b) a spin-disorder scattering regime, which is characterized by a collision-dominated electronic scattering response whose scattering rate $\Gamma$ scales with the magnetic susceptibility; (c) a magnetic polaron (MP) regime, in which the development of an $H$=0 spin-flip Raman response betrays the formation of magnetic polarons in a narrow temperature range above the Curie temperature T$_{\rm C}$; and (d) a ferromagnetic metal regime, characterized by a flat electronic continuum response typical of other strongly correlated metals. By exploring the behavior of the Raman responses in these various regimes in response to changing external parameters, we are able to investigate the evolution of charge and spin degrees of freedom through various transitions in these materials.Comment: 19 pages, 13 figures on 5 pages (Gif format