Soft-mode Spectroscopy In Cubic Batio3 By Hyper-raman Scattering

Hyper-Raman scattering from cubic BaTiO3 is studied to clarify the controversies about the low-frequency dielectric response in this material. Applying the fluctuation-dissipation theorem, we obtain the imaginary part ε′′(Ω) of the dielectric function in the wave-number range from 3 to 150 cm-1. ε′′(Ω) can be adequately described by a classical single-oscillator dispersion formula. In approaching the Curie temperature, we find a continuous decrease of the mode frequency Ω0. The relative damping constant γΩ0 exceeds 2, so that the mode may be referred to as intermediate between oscillator and relaxator. Because of the high damping ε′′(Ω) can be formally written as the sum of two overdamped oscillator contributions. This would lead to the concept of a soft-mode saturation and an extra dispersion mechanism as has been recently inferred from the far-infrared reflectivity spectrum. However, we do not find any evidence for this mode splitting and, so far, regard it as artificial. © 1982 The American Physical Society.26105904591

Temperature Dependence Of Dipolar Modes In Ferroelectric Batio3 By Infrared Studies

Temperature dependence of A1 modes in tetragonal phase and F1u modes in cubic phase of BaTiO3 has been studied by ir (infrared) reflectivity measurements. The spectra have been analyzed using Kramers-Kronig analysis and the coupled-mode classical oscillator fit. The results are in excellent agreement with each other and are compatible with the earlier Raman measurements. Such a compatibility indeed favors the conclusion of Pinczuk et al. with regard to the interpretation of the broad peaks at 270 and 520 cm-1 in the Raman spectrum to be of first order. A critical analysis of the earlier work in BaTiO3 is presented. © 1980 The American Physical Society.2252396240

Laser-excited Fluorescence And Electron-spin Resonance Of Er3+ In Polycrystalline Alcl3

The green fluorescence transitions among the levels corresponding to the 4S3/2 and 4I15/2 configurations of Er3+ diluted in AlCl3 have been measured using laser excitation. The data allow us to determine the crystalline-field splittings of these levels and, in turn, the spin-Hamiltonian parameters. The electron-paramagnetic-resonance spectrum observed at low temperatures is in good agreement with that expected from these parameters. © 1990 The American Physical Society.42190991

High-pressure Raman Study Of Zone-center Phonons In Pbtio3

A complete study of the k=0 optical phonons of the ferroelectric tetragonal PbTiO3 as a function of hydrostatic pressure has been carried out using Raman spectroscopy. The coalescence, to the same frequency, of the high-energy [A1(TO), E(TO)] pairs of phonons in the ferroelectric phase and the disappearance of the first-order Raman lines in the cubic phase has enabled us to determine the transition pressure Pc, as well as the second-order character of the phase transition. Our results also suggest the existence of a tricritical point in the (P,T) phase diagram. Using the Liddane-Sachs-Teller relation we calculate the static dielectric constant as a function of pressure and compare the results with previous dielectric measurements. Moreover, we discuss the soft phonons, their damping, and their behavior near the phase transition. It is found that the soft E(TO) phonon damping function is nearly constant over a wide frequency range and that it appears to diverge near the phase transition. © 1983 The American Physical Society.28127260726

Raman-scattering Study Of Crystal-field Excitations In Pr2cuo4

Crystal-field transitions within the 3H4 multiplet of Pr3+ in Pr2CuO4 were studied by Raman scattering as a function of temperature. We observed three crystal-field excitations at 156, 540, and 675 cm-1. The peak at 156 cm-1, assigned by other authors to the lowest Eg phonon mode, shows a thermal broadening of the linewidth, which is the signature for acoustical-phonon-relaxation processes between crystal-field levels. Our results are in excellent agreement with recent inelastic neutron scattering experiments in Pr2CuO4. © 1994 The American Physical Society.4964391439

Dependence On Volume Of The Phonon Frequencies And The Ir Effective Charges Of Several Iii-v Semiconductors

The mode Grüneisen parameters of the LO and TO Raman phonons of AlN, BN, and BP, and the dependence of eT* on lattice constant have been measured by Raman scattering in a diamond anvil cell. The results for eT* are interpreted by means of pseudopotential calculations of eT* versus lattice constant. © 1983 The American Physical Society.2884579458

Intercalant Vibrations In Stage-1 Alcl3 Graphite

We report the observation of intramolecular vibrations in stage-1 AlCl3-intercalated graphite compounds. The results show that two species are simultaneously present: Al2Cl6 molecules and a layer of solid AlCl3. © 1992 The American Physical Society.461065866588AFOSR; U.S. Department of Energy; DE-AC05-06OR23177; DOE; U.S. Department of Energ

Effects Of Phase Separation On The Magnetization, X-ray Diffraction, And Raman Scattering Of (la1-yndy) 1-xcaxmno3 (y = 0,0.5,1.0;x = 1/3)

Dc-magnetization, x-ray diffraction, and Raman-scattering studies in polycrystalline (La1-yNdy)1-xCaxMnO3 (y = 0.0,0.5,1.0, and x = 1/3) samples are presented. The samples with y = 0.5 and 1.0 show complex magnetic states at low temperatures, with a ferromagnetic coupling strength that weakens with increasing y. X-ray measurements show a single crystallographic phase at all temperatures for y=0.5, with lattice parameter anomalies at temperatures related to electronic and magnetic transitions. The presence of high-frequency vibrational modes in Raman-scattering measurements indicates the existence of charge- and orbital-ordered domains for y = 0.5 and 1.0, which are closely related to the antiferromagnetic component identified by the magnetization experiments. The close relationship between results obtained by magnetic, structural, and optical probes is discussed.636644041644046Wollan, E.O., Koehler, W.C., (1955) Phys. Rev., 100, p. 545Goodenough, J.B., (1955) Phys. Rev., 100, p. 564Chen, C.H., Cheong, S.-W., (1996) Phys. Rev. Lett., 76, p. 4042Radaelli, P.G., Cox, D.E., Marezio, M., Cheong, S.-W., Schiffer, P.E., Ramirez, A.P., (1995) Phys. Rev. Lett., 75, p. 4488Hwang, H.Y., Cheong, S.-W., Radaelli, P.G., Marezio, M., Batlogg, B., (1995) Phys. Rev. Lett., 75, p. 914Coey, J.M.D., Viret, M., Ranno, L., Ounadjela, K., (1995) Phys. Rev. Lett., 75, p. 3910Uehara, M., Mori, S., Chen, C.H., Cheong, S.-W., (1999) Nature (London), 399, p. 560Moreo, A., Yunoke, S., Dagotto, E., (1999) Science, 283, p. 2034. , and references thereinArchibald, W., Zhou, J.-S., Goodenough, J.B., (1996) Phys. Rev. B, 53, p. 14445Zhou, J.-S., Archibald, W., Goodenough, J.B., (1996) Nature (London), 381, p. 770Rao, G.H., Sun, J.R., Liang, J.K., Zhou, W.Y., Cheng, X.R., (1996) Appl. Phys. Lett., 69, p. 424Rao, G.H., Sun, J.R., Liang, J.K., Zhou, W.Y., (1997) Phys. Rev. B, 55, p. 3742Zhou, J.-S., Goodenough, J.B., (1998) Phys. Rev. Lett., 80, p. 2665Ibarra, M.R., Zhao, G.-M., De Teresa, J.M., García-Landa, B., Arnold, Z., Marquina, C., Algarabel, P.A., Ritter, C., (1998) Phys. Rev. B, 57, p. 7446Baszynski, J., Kovac, J., Kowalczyk, A., (1999) J. Magn. Magn. Mater., 195, p. 93Moritomo, Y., (1999) Phys. Rev. B, 60, p. 10374Young, R.A., Sakthivel, A., Moss, T.S., Paiva-Santos, C.O., (1995) J. Appl. Crystallogr., 28, p. 366Radaelli, P.G., Cox, D.E., Marezio, M., Cheong, S.-W., (1997) Phys. Rev. B, 55, p. 3015Huang, Q., Santoro, A., Lynn, J.W., Erwin, R.W., Borches, J.A., Peng, J.L., Ghosh, K., Greene, R.L., (1998) Phys. Rev. B, 58, p. 2684Irwin, J.C., Chrzanowski, J., Franck, J.P., (1999) Phys. Rev. B, 59, p. 9362Abrashev, M.V., Ivanov, V.G., Iliev, M.N., Chakalov, R.A., Chakalova, R.I., Thomsen, C., (1999) Phys. Status Solidi B, 215, p. 631Liarokapis, E., Leventouri, Th., Lampakis, D., Palles, D., Neumeier, J.J., Goodwin, D.H., (1999) Phys. Rev. B, 60, p. 12758Granado, E., Moreno, N.O., García, A., Sanjurjo, J.A., Rettori, C., Torriani, I., Oseroff, S.B., Tokura, Y., (1998) Phys. Rev. B, 58, p. 11435Yoon, S., Liu, H.L., Schollerer, G., Cooper, S.L., Han, P.D., Payne, D.A., Cheong, S.-W., Fisk, Z., (1998) Phys. Rev. B, 58, p. 2795Liu, H.L., Yoon, S., Cooper, S.L., Cheong, S.-W., Han, P.D., Payne, D.A., (1998) Phys. Rev. B, 58, pp. R10115Liu, K., Wu, X.W., Ahn, K.H., Sulchek, T., Chien, C.L., Xiao, J.Q., (1996) Phys. Rev. B, 54, p. 3007Granado, E., Pagliuso, P.G., Sanjurjo, J.A., Rettori, C., Oseroff, S.B., Causa, M.T., Butera, A., Schultz, S., (1998) Non-Crystalline and Nanoscale Materials, pp. 105-115. , edited by J. Rivas and M.A. López-Quintela (World Scientific, Singapore)Granado, E., Sanjurjo, J.A., Rettori, C., Prado, F., Sánchez, R.D., Caneiro, A., Oseroff, S.B., (2000) Phys. Status Solidi B, 220, p. 609Dediu, V., Ferdeghini, C., Matacotta, F.C., Nozar, P., Ruani, G., (2000) Phys. Rev. Lett., 84, p. 4489Adams, C.P., Lynn, J.W., Mukovskii, Y.M., Arsenov, A.A., Shulyatev, D.A., (2000) Phys. Rev. Lett., 85, p. 3954Dai, P., Fernandez-Baca, J.A., Wakabayashi, N., Plummer, E.W., Tomioka, Y., Tokura, Y., (2000) Phys. Rev. Lett., 85, p. 255

Raman scattering studies of monohydrated L-asparagine

Polarized first-order Raman scattering studies at 300 K were carried out in L-asparagine monohydrate crystal in order to obtain the general assignment of its phonon spectra. A careful analysis of the vibrational spectra shows that the assignment of the fundamental vibrational modes can be done on the basis of amino, carboxilic and water groups vibrations, and correlations with previous data reported for other amino acids. However, some vibrations were correctly assigned from the study of its temperature - dependence behavior performed in the range 10 - 300 K. The assignment proposed cofirm the zwitterionic structure of L-asparagine monohydrate crystal.380387Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Phonon Self-energy Effects Due To Superconductivity In Bi2sr2cacu2o8+δ

Raman scattering of A1g phonons in Bi2Sr2CaCu2O8+δ single crystals (δ=0.13, Tc=86 K) has been measured as a function of temperature. We report an anomalous softening in the frequency and a decrease in the linewidth of the A1g phonon at 290 cm-1 (O1,2 c-axis in-phase vibration) below Tc. We also confirm a smaller anomalous softening in the frequency of the A1g phonon at 465 cm-1 (O3 c-axis vibration), but for this phonon mode no linewidth anomaly has been found. We compare the anomalous softening and linewidth behavior in the superconducting state with theoretical calculations for isotropic s-wave, planar d-wave, and dx 2 -y 2 gap symmetries and as for a layered superconductor model.561384268431Thomsen, C., Cardona, M., Gegenheimer, B., Liu, R., Simon, A., (1988) Phys. Rev. B, 37, p. 9860Heynen, E.T., Cardona, M., Karpinski, J., Kaldis, E., Rusiecki, S., (1991) Phys. Rev. B, 43, p. 12958Kendizora, C., Kelley, R.J., Onellion, M., (1996) Phys. Rev. Lett., 77, p. 727Macfarlane, R.M., Rosen, H., Seki, H., (1987) Solid State Commun., 63, p. 831Ruf, T., Thomsen, C., Liu, R., Cardona, M., (1988) Phys. Rev. B, 38, p. 11985Burns, G., Chandrashekhar, G.V., Dacol, F.H., Strobel, P., (1989) Phys. Rev. B, 39, p. 775Bokholt, M., Erie, A., Splittgerber-Hünnekes, P.C., Güntherodt, G., (1990) Solid State Commun., 74, p. 1107Leach, D.H., Thomsen, C., Cardona, M., (1993) Solid State Commun., 88, p. 457Martin, A.A., Lee, M.J.G., (1995) Physica C, 254, p. 222Liu, R., Klein, M., Han, P.D., Payne, D.A., (1992) Phys. Rev. B, 45, p. 7392Menéndez, J., Cardona, M., (1984) Phys. Rev. B, 29, p. 2051Litvinchuk, A.P., Thomsen, C., Cardona, M., (1992) Solid State Commun., 83, p. 343Zeyher, R., Zwicknagl, G., (1990) Z. Phys. B, 78, p. 175Nicol, E.J., Jiang, C., Carbotte, J.P., (1993) Phys. Rev. B, 47, p. 8131Devereaux, T.P., (1994) Phys. Rev. B, 50, p. 10287Kendziora, C., Rosenberg, A., (1995) Phys. Rev. B, 52, pp. R986