Harukazu Yoshino

Pressure transmitting medium Daphne 7474 solidifying at 3.7 GPa at room temperature

A pressure transmitting medium named Daphne 7474, which solidifies at P(s)=3.7 GPa at room temperature, is presented. The value of P(s) increases almost linearly with temperature up to 6.7 GPa at 100 degrees C. The high pressure realized by a medium at the liquid state allows a higher limit of pressurization, which assures an ideal hydrostatic pressure. We show a volume change against pressure, pressure reduction from room to liquid helium temperature in a clamped piston cylinder cell, pressure distribution and its standard deviation in a diamond anvil cell, and infrared properties, which might be useful for experimental applications.

Solidification of high-pressure medium daphne 7373

The solidification pressure of Daphne 7373, which is widely used as a pressure medium in high pressure studies, was examined at room temperature. Using a new generation clamp-type pressure cell, we found that Daphne 7373 solidifies at 2.2 GPa at room temperature. This is exactly on the natural extrapolation of the melting curve obtained at lower pressures and temperatures in our previous report. The solidification pressure of Daphne 7373 is twice as high as that of another well-known medium Fluorinert 77/70 (0.9 GPa). This allows us to hold hydrostatic pressure even in the newly developed BeCu–NiCrAl clamp-type pressure cell, which exceeds the limit of 1.5 GPa generated by a conventional BeCu cell.

High-Pressure Research in Organic Conductors

High-pressure studies on organic conductors and superconductors are reviewed. It is stressed that almost all the organic conductors are studied by means of high pressures, but the role or meaning o...

Low temperature electric nature of τ-phase conductors

Magnetoresistance, magnetization, and reflectance spectra were measured for τ-(EDO-S,S-DMEDT-TTF) 2 (AuBr 2 ) 1+y , (y∼0.75) (EDO-S,S-DMEDT-TTF = ethylenedioxy-S,S-dimethylethylenedithio-tetrathiafulvalene) and τ-(P-S,S-DMEDT-TTF) 2 (AuBr 2 ) 1+y , (y∼0.75) (P-S,S-DMEDT-TTF = pyrazino-S,S-dimethylethylenedithio-tetrathiafulvalene). The saturation of magnetization curve and Drude dispersion imply the weak ferromagnetic and metallic nature of former compound at low temperature. For the comparison with this compound, magnetoresistance of latter salt was measured up to 24 T.

Transport properties of HMTSF-TCNQ up to 8 GPa and a novel hysteresis and quantum oscillatory behavior in magnetoresistance in magnetic field up to 31 Tesla

With the interest of ground state near CDW at low temperature, the electronic properties under high pressure, at low temperature and in high magnetic field of HMTSF-TCNQ are examined. Up to 8 GPa, the overall resistivity-temperature behaviour are unchanged, i.e. broad resistance minimum around 100–150 K and subtle resistance decrease below around 30 K. The pressure insensitive nature is not consistent with previous data. At 1.5–1.6 GPa, but not at P = 0, a novel hysteretic behaviour and probable quantum oscillations in magnetoresistance are found in a clear form.

Field-Induced Successive Phase Transitions in the Charge Density Wave Organic Conductor HMTSF-TCNQ

The magnetoresistance of quasi-1D two-chain organic conductor HMTSF-TCNQ (hexamethylenetetraselenafulvalene-tetracyanoquinodimethane), which shows charge density wave transition at ambient pressure, was studied under pressure up to 27 T and 31 T, in two high field facilities. We found a kink structure in the magnetoresistance reminiscent of field-induced spin density wave at an intermediate pressure of 1.5 GPa between 0 and 2 GPa. We speculate that these are successive quantum phases induced by magnetic field.

Giant Shubnikov-de Haas oscillation and the new metallic state in the organic τ-type conductors

Two-dimensional organic T-type conductors show metallic temperature dependence of resistivity down to T min = 30-50 K, below which a resistivity upturn is observed. A large negative magnetoresistance appears below T min suddenly in temperature. Below about 4 K, magnetoresistance in any direction is extremely hysteretic in field-, temperature- or field-angle-sweep, and p⊥(H//plane) shows switching between two- and four-fold depending on magnetic and thermal history, indicating magnetic domain generation. Static susceptibility shows slight ferromagnetic component. NMR is in favor of anti-ferromagnetism below about 15 K. These two results imply that the system is a weak ferromagnetic one. Preliminary optical reflectance and specific heat studies implied metallic state at low temperature, but no clear-cut proof has been shown whether or not the ground state is metallic. This report presents giant Shubnikov de Haas (SdH) oscillation in both τ-(EDO-S,S-DMEDT-TTF) 2 (AuBr 2 ) 1+y , and τ-(P-S,S-DMEDT-TTF) 2 (AuBr 2 ) 1+ν , (y ∼ 0.75), which is a clear evidence for the metallic ground state. However, the observed Fermi surfaces (FS) are 0.65 and 6.1% of the first Brillouin zone for T-(EDO-S,S-DMEDT-TTF) 2 (AuBr 2 ) 1+ν , and 2.3 and 6.9% for τ-(P-S,S-DMEDT-TTF) 2 (AuBr 2 ) 1+y , (y ∼ 0.75), which suggest extremely small FS pockets, and were not expected by the previous band calculation. Further, it is surprising that the Dingle temperature was around 1 K, indicating unexpectedly clean, while residual resistivity ratio is about 1. We note that the fundamental oscillation of 0.65% is already n = 2 state, which is already next to the Landau quantum limit.

New donor molecules and their τ-phase conducting salts

The unsymmetrical donor molecules pyrazino-R,R-dimethylethylenedithio-tetrathiafulvalene, ethylenedioxy-R,R-dimethylethylenedithiotetrathiafulvalene, pyrazino-S,S-dimethylethylenedithio-diselenadithiafulvalene, and pyrazino-S,S-dimethylethylelenediselenotetrathiafulvalene as well as some of their conducting salts of τ-phase with Aul 2 and/or AuBr 2 anions were prepared and studied.

Direct evidence of dimensionality enhancement of Q1D TMTSF and DMET salts

Magnetoresistance measurement was carried out for quasi-one-dimensional (Q1D) organic superconductors, (TMTSF) 2 PF 6 , (DMET) 2 AuI 2 and (DMET) 2 I 3 at 1.2 K up to about 15 kbar. The third angular effect (TAE) is observed in their metallic state as an hump anomaly of the angular dependence of the magnetoresistance. It has been found that the angular width of the TAE hump anomaly increases with increasing hydrostatic pressure. This is the first direct evidence of the dimensionality enhancement by pressure for the Q1D superconductors, where the dimensionality is defined as the anisotropy of the transfer integrals, t y /t x .

Monoanionic and neutral tris(dialkylthiotetrathiafulvalenyldithiolato) vanadium complexes

Tetraethylammonium tris[diethylthio-, di(n-butylthio)- or trimethylenedithio-tetrathiafulvalenyl(TTF)dithiolato] vanadium complexes (NEt 4 +1a,b,c - ) were oxidized with iodine to give the corresponding neutral complexes (1a,b,c), in which one unpaired electron is preferentially distributed at the TTFdithiolato groups. The compressed pellets of 1a,b,c exhibited comparatively low room-temperature electrical conductivities (σ RT s) of 10 -(4-8) S cm -1 , which are however higher by 10 2-6 times than that (<10 -10 S cm -1 ) in a neutral bis(5,6-dihydro-1,4-dithiin-2,3-dithiolato) vanadium complex, V(DDDT) 3 .