Gunzi Saito

Determination of SDW Characteristics in (TMTSF)2PF6 by 1H–NMR Analysis

The static properties of spin density waves (SDW) in (TMTSF) 2 PF 6 were determined by a precise analysis of 1 H-NMR lineshape in the low temperature SDW state. The observed angular dependence of lineshape was well reproduced by a picture of incommensurate sinusoidal SDWs. The wave number was found to be (0.5, 0.24±0.03, -0.06±0.20) in the units of a * , b * and c * . This value is very near the optimal nesting vector recently calculated. The SDW amplitude at low temperature was estimated as 8% µ B /molecule.

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

Electrical properties and crystal structures of mercury (II) thiocyanate salts based upon BEDTTTF with Li+, K+, NH+4, Rb+, and Cs+

Abstract A new series of BEDTTTF salts with a cation (Li + , K + , NH + 4 , Rb + , or Cs + ) as well as an anion [Hg(SCN) 4 ] 2- , was prepared. The crystal structures and the electrical properties were investigated with changing the cation from Li + (0.73 A) to Cs + (1.70 A). The superconductivity of (BEDTTTF) 2 [NH 4 Hg(SCN) 4 ] was confirmed at 0.8 K by the electrical transport measurements.

Ambient-pressure superconductivity at 8 K in the organic conductor β-(BEDT-TTF)2I3

Abstract We report that the superconductivity with the onset temperature as high as 8 K in the organic conductor of β-(BEDT-TTF)2I3, which was achieved by an application of a soft pressure, i.e. 1.3 kb, remains stable with even higher transition temperature after a subsequent release of pressure to the ambient pressure. Correspondingly, higher values of the upper critical field, Hc2, are observed. (Hc2 > 20 k0e at 2 K along the c∗-axis.)

Switching effect in organic charge transfer complex crystals

A reproducible current switching effect has been observed in various mixed‐stack organic charge transfer crystals whose ionicities are close to the neutral‐ionic phase boundary. This effect appears to be related to the intrinsic nonlinear conductivity, which has recently been reported in these crystals. This switching has a reasonably large delay time and our results indicate that it is a bulk property of the crystals. Discussion is given on the possible mechanism of this effect.

Ambient-pressure superconductivity in organic metals, BEDT-TTF trihalides

Abstract The ambient-pressure superconductivity in β-(BEDT-TTF) 2 I 3 and its mixed trihalide homologues has been studied, where BEDT-TTF is bis-(ethylenedithio-tetrathiafulvalene. In β-(BEDT-TTF) 2 I 3 , two superconductivity states are observed, i.e. , a low- T c state with T c = 1.1 – 1.5 K and a high- T c state with T c = 7 – 8 K. The high- T c state, which was originally discovered under a pressure of 1.3 kbar, is found to remain stable after removal of pressure. Moreover it has also been observed even without application of pressure. In order to realize an intrinsic high- T c ambient-pressure organic superconductor, we propose an introduction of ‘lattice pressure’ by substitution of triiodide anion (I 3 − ) with smaller mixed trihalide anions, such as I 2 Br − and IBr 2 − . The result is discussed using a model based on the T c vs. pressure phase diagram for β-(BEDT-TTF) 2 I 3 .

Resonant Raman scattering in organic conductors α and β-(BEDT-TTF)2X (X=I3 and IBr2)

Abstract Molecular vibrations in the crystals of organic conductors α and β-(BEDT-TTF) 2 X, (X=I 3 , IBr 2 ), a neutral donor BEDT-TTF, and acceptors n-Bu 4 N·I 3 and n-Bu 4 N·IBr 2 are investigated by Raman scattering. Strong Resonant effects are observed in the I 3 compounds, when the incident laser wavelength approaches the optical transition energy of the I 3 anion. More than ten overtones of the symmetric stretching mode of anions appear. For the modes related to the C=C vibrations the decrease of peak energies and their broadening are observed in the charge-transfer salts.

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.

Spectroscopic Study Of The Neutral-To-Ionic Phase Transition In Ttf-Chloranil

Abstract Infrared reflectance spectra have been investigated on TTF-chloranil single crystals near the neutral-to-ionic phase transition temperature TC. It was confirmed that abrupt changes in the ionicity and the stack dimerization take place simultaneously at TC. The effect of an external electric field and light irradiation upon the dimerized lattice below TC has been investigated by reflectance measurements.

A new ambient pressure organic superconductor (BEDT-TTF)2Cu(NCS)2 with Tc above 10 K

An ambient pressure superconductivity in (BEDT-TTF)2Cu(NCS)2 is reported. The superconducting critical temperature is the highest among the organic superconductors so far obtained (Tc=10.4 K). The salt prepared using deuterated BEDT-TTF is also an ambient pressure superconductor with a slightly higher Tc (11.0K). The crystal structure analysis and resistivity measurement revealed the highly two-dimensional nature of this salt. The temperature dependence of normal resistivity, superconducting critical field, quantum oscillation of resistivity and so on are reported down to 0.5 K and up to 13.5 T. The superconducting upper critical field shows a peculiar temperature dependence, and the parallel critical field behaviour is ascribed to the dimensional crossover effect. The quantum oscillation is understood as the Shubnikov-de Haas effect, and the possible Fermi surface is presented. The possible superconducting mechanisms are also discussed.