K. Yakushi

Polarized reflectance spectrum of β-(BEDT-TTF)2I3 single crystal

Abstract The polarized reflectance spectrum of β-(BEDT-TTF) 2 I 3 was measured over the spectral region from 720 cm −1 to 25,000 cm −1 . The optical conductivity spectrum showed an infrared band strongly polarized along the [110] axis. This is concluded to be due to an inter-band transition across the band gap. Discussion is given on the band

Evolution of superconductivity of KxC60 upon K-doping : microwave low-field signal and ESR study

Abstract By means of low magnetic-field micowave absorption (Low-Field Signal) and conventional ESR, we have studied the evolution of superconductivity in bulk KxC60 dependent on the variation of K- doping temperature and time. The first LFS as an occurrence of superconductivity is observed in a doping time as short as td = 0.5 h with a discrete Tc ∼ 19 K, and the volume of the superconducting phase increases on further dopings, while Tc changes slightly. The sample in a superconducting state exhibits strong ESR absorptions, which indicates the presence of a non-superconducting metallic phase coexisting with a superconducting phase in inhomogeneously doped KxC60. These phases are closely correlated and disappear at the same time by overdoping.

Temperature dependence of the reflectance spectrum of β-(BEDT-TTF)2I3

Abstract The temperature dependence of the polarized reflectance spectrum of β-(BEDT-TTF) 2 I 3 was measured over the spectral range from 750 cm −1 to 25,000 cm −1 . The plasma frequency and the relaxation rate were obtained by analyzing the low-temperature spectra. The absolute value and the anisotropy of the optical conductivity at low temperature agree with those of the dc conductivity within the experimental error. The dimensionless electron-phonon coupling constant was estimated to be 1.6 from the temperature dependence of the relaxation rate.

The polarized reflectance spectrum of a novel organic conductor (BEDT-TTF)2ClO4(C2H3Cl3)0.5

Abstract The polarized reflectance spectrum of a novel organic conductor, (BEDT-TTF) 2 ClO 4 (C 2 H 3 Cl 3 ) 0.5 was measured at room temperature over the spectral region from 340 cm -1 to 25000 cm -1 . The reflectance spectrum provided an evidence for the anisotropic two-dimensional character of this material. The optical conductivity spectrum exhibits the existence of an optical band gap of about 0.2 eV, suggesting that this material is a semimetal rather than a metal.

Low-temperature reflection spectrum of K-TCNQ single crystal

Abstract Polarized reflection spectra of a K-TCNQ single crystal have been measured at 27,295 and 413 K. The absorption spectra were derived from the observed reflection spectra by Kramers-Kronig transformation. At 27 K, the near-infrared absorption band which is associated with the charged transfer between TCNQ − ions, splits into a strong sharp peak at 8 × 10 3 cm −1 and a weak broad band at 11 × 10 3 cm −1 . These bands were interpreted in terms of the strongly correlated extended Hubbard model including the nearest-neighbor Coulomb interaction.

Reflectance spectra of β -, θ -, and κ-(BEDT-TTF)2I3, and β″- and β′-(BEDT-TTF)2ICl2: Relation between the inter-band transition and the dimeric structure

Abstract The polarized reflectance spectra of the single crystals of the title compounds were measured at room and low temperatures. The correlation was found between the appearance of the extra electronic transitions overlapped on the Drude-tail and the dimeric arrangement of BEDT-TTF. From this relation, this extra transition was assigned to the inter-band transition between the split bands due to the strong dimeric interaction. The Drude parameters were determined by analyzing the low-temperature spectra taking account of the inter-band transition.

Polarized reflectance spectrum of β-(BEDT-TTF)2PF6

Abstract The polarized reflectance spectrum of β-(BEDT-TTF) 2 PF 6 was measured over the spectral range from 720 cm −1 to 25, 000 cm −1 at 293 K (semiconductive phase) and at 318 K (metallic phase). The infrared band found in the conductivity spectrum, which was obtained by the Kramers-Kronig transformation of the reflectance data, is interpreted as the one associated with inter-band transition.

Reflectance Spectra of Bedt-Ttf salts

Abstract The polarized relectance spectra were measured on four BEDT-TTF salts. The results clearly show the effects of intermolecular s-s interaction which gives more or less tow dimensional character in their band structures. The observed infrared maxima in the conductivity spectra are concluded to be attributable mainly to the inter-band excitation.

Preparation, structure and properties of metallic (phthalocyanato)nickel salts

Abstract Highly conducting materials of (phthalocyanato)nickel hexafluoroarsenate, (NiPc) 2 AsF 6 , and hexafluoroantimonate, (NiPc) 2 SbF 6 , were prepared by the use of an electrochemical technique. The crystal structures resemble that of NiPc(I 3 ) 0.33 , which is composed of NiPc molecular columns encompassed by triiode anions. The electrical conductivity of these salts exhibits a metallic behavior at least down to 200 K. It was concluded from the ESR experiment that (NiPc) 2 SbF 6 is a doubly mixed valence compound.

X-ray photoelectron spectroscopy of tetramethyltetraselenafulvalene (TMTSF) complexes

Abstract X-Ray photoelectron spectra, in particular, in their Se3d and 3p regions are studied on (TMTSF) 2 X (X= PF 6 , AsF 6 , ClO 4 , IO 4 and BF 4 , TMTSF · TCNQ and TMTSF·DDQ. TMTSF·TCNQ (black form) and TMTSF·DDQ are concluded to be in a mixed valence state, whereas TMTSF·TCNO (red form) is a neutral charge-transfer complex. In the cases of (TMTSF) 2 X salts, the Se3d peak is sharp without any indication of the broadening associated with the mixed valence character. It is suggested that charges are equally distributed over TMTSF molecules.