Hiromi Taniguchi

The C=C Stretching Vibrations of κ-(BEDT–TTF)2Cu[N(CN)2]Br and Its Isotope Analogues

The C=C stretching modes in resonance Raman spectra and infrared reflectivity were measured at temperatures between 15 K and 300 K using various polarizations in κ-(BEDT–TTF) 2 Cu[N(CN) 2 ]Br, its fully and partially deuterated analogues, and 13 C-substituted analogue. The infrared- and Raman-active bands were re-assigned based on the factor group analysis. We found a Raman-active EMV-coupled ν 3 mode near 1420 cm -1 , which shows a large downshift and broadening through the inter-dimer EMV interaction. The mixing of the bridge and ring C=C stretching vibrations depend upon the symmetry of the crystal mode. In contrast to deuterated crystals, the non-deuterated crystals show a splitting in the ν 2 , ν 3 , and ν 27 bands.

Anomalous Pressure Dependence of Superconductivity in Layered Organic Conductor, κ-(BEDT-TTF)4Hg2.89Br8

The P–T phase diagram and transport properties of a layered organic superconductor, � -(BEDTTTF)4Hg2:89Br8, which can be viewed as a nealy half-filled band system, are reported. Through careful resistivity measurements under pressures of up to 4.5 GPa, we uncovered anomalous pressure dependence of Tc of this superconductor, including a peak structure at approximatly 0.7 GPa and a minimum structure at higher pressure. The normal-state resistivity showed T-linear behavior at low pressures and this behavior gradually transformed into T-squared behavior with increasing pressure. The pressure, Pc � 2 GPa, at which Tc has a turning value, corresponds to the onset of the T-squared behavior.

Emergence of charge degrees of freedom under high pressure in the organic dimer-Mott insulator β′-(BEDT - TTF) 2 ICl 2

To elucidate the pressure evolution of the electronic structure in an antiferromagnetic dimer-Mott (DM) insulator

Electronic specific heat of BEDT-TTF-based organic conductors

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Resistive transition in an extremely two-dimensional superconductor, α-(BEDT-TTF)2NH4Hg(SCN)4

-(BEDT-TTF)

Short piston-cylinder pressure cells based on Ni–Cr–Al cylinders and their application to fragile materials

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Phase control of strongly correlated organic conductor

ICl

Magnetization and ac susceptibility in the vortex state of κ-(BEDT-TTF)2Cu[N(CN)2]Br

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Magnetic-field-induced superconductor-insulator-metal transition in an organic conductor : An infrared magneto-optical imaging spectroscopic study

, which exhibits superconductivity at 14.2 K under 8 GPa, we measured the polarized infrared (IR) optical spectra under high pressure. At ambient pressure, two characteristic bands due to intra- and interdimer charge transfers have been observed in the IR spectra, supporting that this salt is a typical half-filled DM insulator at ambient pressure. With increasing pressure, however, the intradimer charge transfer excitation shifts to much lower energies, indicating that the effective electronic state changes from half-filled to 3/4-filled as a result of weakening of dimerization. This implies that the system approaches a charge-ordered state under high pressure, in which charge degrees of freedom emerge as an important factor. The present results suggest that charge fluctuation inside of dimers plays an important role in the high-temperature superconductivity.

High-Pressure Studies of Doped-Type Organic Superconductors

Abstract Thermodynamic studies for a series of partially deuterated κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Br single crystals were performed in order to see variation of the normal-state density of sates around the two-dimensional Mott transition caused by the bandwidth control. The electronic specific heat coefficient γ was found to decrease monotonously when the system approaches the boundary from the metallic region. The Brinkman–Rice-type mass enhancement is absent near the critical boundary.