N. Ogita

Raman scattering study of hexaboride crystals

Abstract The valence-dependent Raman scattering spectra has been found for the RB6 crystals (R=Ca2+,Yb2+, Ce3+, Pr3+, Gd3+, and Dy3+). In the divalent crystals of CaB6 and YbB6, Eg phonon shows doublet, while the line shape is a broad single peak for the trivalent case. Since both doublet peaks satisfy the selection rule due to the cubic symmetry, the doublet spectra is not explained by the structural phase transition, but by the anisotropic charge distribution on B6. In the trivalent crystals, the two kind of the extra peaks have been commonly observed at around 200 cm −1 and at around 1400 cm −1 . The peak intensities of the former decrease with decreasing temperature, and their peak energies increase with increasing lattice constant. These anomalous features are well explained by the vibration of R ion in the oversized cage space formed octahedral B6 molecule. Thus, this new excitation can be attributed to a local vibration of the R ion, which can be regarded as “rattler.”

Optical conductivity of rattling phonons in type-I clathrate Ba 8 Ga 16 Ge 30

A series of infrared-active optical phonons have been detected in type-I clathrate

Phonon Raman scattering of Sr2RuO4

{text{Ba}}_{8}{text{Ga}}_{16}{text{Ge}}_{30}

Low-energy optical phonon modes in the caged compound LaRu2Zn20

by terahertz time-domain spectroscopy. The conductivity spectra with the lowest-lying peaks at 1.15 and 1.80 THz are identified with the so-called rattling phonons, i.e., optical modes of the guest ion

Interplay between low-energy optical phonon modes and structural transition in PrT2Zn20 (T=Ru and Ir)

{text{Ba}}^{2+}(2)

Raman scattering investigation of β-pyrochlore osmium oxides, AOs2O6 (A=K, Rb, and Cs)

with

Raman Scattering Investigation of Skutterudite Compounds

{T}_{1u}

Crystal field excitations of filled skutterudite PrRu4P12 by Raman scattering

symmetry in the oversized tetrakaidecahedral cage. The temperature dependence of the spectra from these modes are totally consistent with calculations based on a one-dimensional anharmonic potential model that, with decreasing temperature, the shape becomes asymmetrically sharp associated with a softening for the weight to shift to lower frequency. These temperature dependences are determined, without any interaction effects, by the Bose factor for optical excitations of anharmonic phonons with the nonequally spaced energy levels.

Phonon and electronic excitation study of CeRhSb and CeNiSn by Raman scattering

Phonon Raman scattering spectra of Sr2RuO4 have been measured in the temperature region between room temperature and 5 K. Three symmetry-allowed phonons have been observed at room temperature. Since similar spectra have been observed at low temperature, Sr2RuO4 does not undergo structural phase transitions in the temperature region. The energy of the phonon modes has been calculated by a GF matrix method. The force constants along the c-axis of Sr2RuO4 are larger than those for La2−xSrxCuO4.

Raman scattering of CuGeO3

The caged compound LaRu2Zn20 exhibits a structural transition at TS =150 K, whose driving mechanism remains elusive. We have investigated atomic dynamics by the measurements of specific heat C and inelastic X-ray scattering (IXS). The lattice part of the specific heat Clat divided by T3, Clat/T3, shows a broad peak at around 15 K, which is reproduced by two Einstein modes with characteristic temperatures of 35 K and 82 K, respectively. IXS measurements along the [111] and [110] directions reveal optical phonon modes at 3 meV (35 K) and 7 meV (80 K), respectively, whose values agree with the values of Einstein temperatures. The first principles calculation has assigned the phonon modes at 3 meV as the optical modes of Zn atoms located at the middle of two La atoms. The low-energy vibration of the Zn atom perpendicular to the there-fold axis is thought to lead the structural instability of LaRu2Zn20.