R. Merlin

Resonant two magnon Raman scattering in α-Fe2O3

Abstract Strong resonant enhancement of two-magnon Raman scattering was observed in antiferromagnetic α-Fe 2 O 3 for laser frequencies near the intrinsic absorption edge. One magnon scattering, although allowed by symmetry, was not observed. The laser frequency dependence of the resonance enhancement could be well presented by the square of the magnitude of the first derivative of the electric susceptibility. Based on these facts, we conclude that the scattering arises from an exchange mechanism in the excited state.

Raman scattering in the high Tc superconductors MBa2Cu3O7-x

Abstract We report Raman scattering measurements of MBa 2 Cu 3 O 7 ( M = Y , Sm , Eu ) polycrystalline superconductors in the region of Cu-O stretching vibrations. Four peaks are seen. On the basis of the factor group analysis given here they are assigned to two Raman allowed and two ir-allowed LO modes. The latter are probably induced by disorder (e.g. O-vacancies).

Subband-Landau-level coupling in tilted magnetic fields: Exact results for parabolic wells

Abstract The problem of quasi-two-dimensional electrons in magnetic fields at arbitrary orientations is solved analytically for parabolic wells. The energy spectrum reveals features that are not apparent in results based on perturbation theory.

Inelastic light scattering by electronic excitations in semiconductor heterostructures

In recent years there has been much research on inelastic light scattering by quasi-2-D electron systems in quantum wells and heterostructures. In this paper we present a general description of resonant inelastic light scattering as a spectroscopic method that reveals single particle and collective behavior of electrons and holes in semiconductor microstructures and review some of the more recent work. We consider high-mobility two-dimensional free carrier systems in modulation doped GaAs-(AlGa)As heterostructures, purely space-charge induced quantum wells of GaAs and shallow impurities in GaAs- (AlGa)As quantum wells.

Optic phonon anomalies and f-d hybridization in SmS and SmB6

Abstract The optic phonons of semiconducting SmS and of (homogeneously) mixed-valent SmS and SmB6 have been investigated by means of Raman scattering. The dominant electron - phonon interaction upon resonantly exciting the 4f shell is revealed as a coupling of the strongly localized 4f hole at the Sm site to full symmetric (Aj g) displacements of the nearest neighbour anions i.e. mainly to LO(L) phonons. Semiconducting and mixed-valent, metallic SmS show a “softening” of the LO(L) phonon frequencies with respect to the other divalent and trivalent rare earth sulfides, respectively, going in parallel with a “softening” of the bulk modulus. The f-d hybridization is considered as the common origin of these phonon frequency renormalizations.

TWO MAGNON RESONANT RAMAN SCATTERING IN TRANSITION METAL OXIDES

Resonant Raman scattering by two magnons is reported for the Ar-+ 4T2 absorption band of o-FeaOs but is absent for the corresponding band of FeBOs. This is related to the absence of inversion symmetry in the former and its presence in the latter compound. The absorption edge of NiO at m3.6 eV shows strong resonance for phonons but not for magnon processes. From this fact if is conjectured that the edge is due to O(2p)-+ Ni(3d) transitions. In this letter we present results on the resonant scattering of light by two magnons in the antiferro-magnetic transition metal compounds cw-Fe,O,, FeB03 and NiO. The optical properties of FeB03 have been well studied [ 11. There is a broad absorption band centered at 2.05 eV due to transitions from the 6Ars( S) to the 4Tzs(4G) manifolds [ 11. These transitions occur at 1.98 eV in cw-Fe,O, [2]. The two-magnon spectra of both compounds are also well known [3,4]. We have measured the intensity of the two-magnon scattering as a function of laser frequency. The results for o-Fez-O3 are shown in fig. 1. The corresponding results for FeB03 are not shown because the two-magnon Raman scattering cross section is nearly a constant in the same optical region. The cross section of the two-magnon line can be obtained following Loudons derivation [5]. The corresponding scattering tensor has the form /(E,-Cd-iq)(E, + s2-0-irl) , (1) where

Suppression of Raman scattering by interface phonons in quantum wells under high photoexcitation

i and

Raman scattering in a magnetic semiconductor

j are the ground state orbitals of ions i and j,

Phonon Raman scattering from spin superstructures: Magnetic “Bragg” scattering

J and

Reply to “comments on the paper ‘anti-stokes luminescence in Europium monochalcogenides’”

,, are the corresponding excited state orbitals with energies E, and E,,. The laser energy is denoted by w, the two-magnon energy by 51, erk,l are the components of the electric dipole operator. If one confines the summation to nearly degenerate intermediate states (E, NE,,) and, moreover, if the exchange matrix element is assumed isotropic and independent of the intermediate state, it is possible to transform 83