Etsuyuki Matsuura

Raman scattering in layered compound 2H-WS2

Raman scattering of layer-type compound 2H-WS2 has been studied at room temperature. The first-order Raman peaks are observed at 27.4, 357 and 423 cm-1. The low-frequency peak at 27.4 cm-1 is a rigid-layer mode, from which the interlayer shear force constant is estimated. The central force model is applied to the high-frequency phonons. The interlayer shear force constant is much smaller than the intralayer force constants. We also find several peaks due to the second-order processes.

Raman scattering of NiS2

Abstract Raman scattering measurements of NiS2 is done and five optical phonon peaks are found. These peaks are assigned to Ag, Eg and 3Tg phonons which are all of the Raman active optical phonons in pyrite-type crystal. The results are compared with those of FeS2 and MnS2.

Hall effect and transverse magnetoresistance in a low-dimensional conductor HfTe5

Abstract Temperature dependence of Hall coefficient and transverse magnetoresistance of a low-dimensional conductor HfTe 5 with 1.5 wt. % Zr is reported for the first time up to 12 kOe in magnetic field. Hall coefficient changes sign from positive to negative at the temperature at which the peak of the resistivity has been observed. Temperature dependence of the transverse magnetoresistance has an anomaly. Two-carrier model has been proposed to explain the data qualitatively. These results suggest the change of the electronic structure associated with the charge density wave formation or some other kind of phase transition. Simple chemical bonding consideration shows that the carrier originates from p-like bands.

Anomalous electrical resistivity in HfTe5

Abstract The group IVB transition-metal pentachalcogenide, HfTe 5 , exhibits a peak of the electrical resistivity in the vicinity of 76 K.

Study of the Infrared Properties of (La1-xSrx)2CuO4

Reflectivity and transmission spectra of (La1-xSrx)2CuO4 were measured in the spectral range of 20-4800 cm-1. The intensity of the absorption peak around 255 cm-1 became twice with lowering temperature from 298 to 19 K accompanying weak softening, while the Cu-O asymmetric stretching mode at 510 cm-1 was almost unchanged both in its energy and intensity. The origin of the soft-phonon mode is discussed.

Raman study of charge-density-wave phase transition in quasi-one-dimensional conductor (TaSe4)2I

Abstract Polarized Raman spectra were obtained in the quasi-one-dimensional conductor (TaSe4)2I above and below the charge-density-wave (CDW) transition temperature (Tc=263 K). The Raman intensities of many peaks become intenser and two of the phonon peaks shift to higher frequency with decreasing temperature. Moreover a new broad peak at about 90 cm−1 and a new peak around 166 cm−1 appear in the low-temperature phase. The polarization characteristic shows that the former is assigned to totally symmetric mode. The damping constant of the phonon at 90 cm−1 increases markedly with increasing temperature. The frequency shifts to higher frequency as the temperature increases and the coupling coefficient is approximately proportional to (Tc−T) 1 2 . This peak becomes Raman active owing to the CDW phase transition. The temperature dependence of the damping constant and the frequency shift may have a relation to the dynamical properties of the CDW phase transition.

Electrical and thermal properties in CuV2S4

Abstract The successive phase transitions of the cubic spinel structure CuV 2 S 4 have been studied by the electrical resistivity and the specific heat. In the resistivity and the specific heat two anomalies have been observed at T 1 ∼91 K and T 3 ≈55 K. The specific heat indicates that the phase transition at T 1 is in the vicinity of a tricritical point, where the resistivity has a small sharp peak. On the other hand, the specific heat shows a step at T 3 , where a hysteresis of the resistivity indicates the existence of the first-order phase transition.

Shubnikov-de Haas oscillations and Fermi surfaces in transition-metal pentatellurides ZrTe5 and HfTe5

Shubnikov-de Haas (SdH) oscillations are reported for well characterised crystals of the anisotropic conductors ZrTe5, HfTe5 and Hf0.88Zr0.12Te5. In each material, only one cross sectional frequency dominates the oscillations below the temperature of the resistivity anomaly. Shapes of the Fermi surface (FS) are deduced from the dependence of the extremal FS cross sections on the angle between the crystallographic axes of the sample and the magnetic field. The FS obtained is a long cigar-shaped ellipsoid, which indicates the quasi-two-dimensional character of the electronic properties in these pentatellurides. The temperature dependence (0.32<T<4.2 K) of the amplitudes of the SdH oscillations has been studied to determine the cyclotron effective masses for dominant FS cross sections. The high-field Hall coefficient at 1.2 K shows clearly that at least two types of electrons contribute to the low-temperature conduction. The observed FSS in ZrTe5 and HfTe5 supply 78 and 68% of the total carriers estimated from the high-field Hall coefficient. The conductivity calculated by using the values of the carrier density and the Dingle temperature is the major part of the conductivity at low temperatures in ZrTe5 and HfTe5. Low-temperature electronic band structure is discussed on the basis of the electronic band calculation of Whangbo et al. (1982).

Strong Resistivity Anomaly in a New Low-Dimensional Conductor HfTe5

Abstract Temperature dependence of the resistivity, Hall coefficient and magnetic susceptibility of HfTe5 with 1.5 wt. %, Zr is reported. Anisotropic large diamagnetism is reported and has the peak in the vicinity of 76 K. Temperature dependence of Hall coefficient under 117 kOe elearly shows the destruction of Fermi surface at about 90 K. HfTe5 can be considered to be a semimetal and observed resistivity anomaly may be accompanied by the CDW formation along c-axis. We also discuss the mixed crystal effect with ZrTe5 and present the data of quantum oscillation observed at low temperature.

Superconducting Properties of La1.85Sr0.15CuO4 Made by Hot-Press and Sinter Methods

The superconducting transition properties were investigated by resistivity and magnetization in La1.85Sr0.1CuO4 for hot-pressed and sintered samples. The zero resistance at 34.5 K and the midpoint of the transition at 37.7 K were obtained in the sintered one with the onset temperature of 42 K. A single crystal was obtained in the hot-pressed one.