Ryusuke Kondo

Uniaxial strain method for soft crystals: Application to the control of the electronic properties of organic conductors

We developed the uniaxial strain method to compress a crystalline sample along any direction without involving Poisson’s effect. The uniaxial strain is realized by inserting a composite of either the sample embedded in epoxy or the sample in frozen oil into a cylinder much harder than the sample composite followed by the application of external forces to a piston put on the sample composite. We verified, by using a strain gauge embedded in the epoxy or the frozen oil, that the strain thus created has the uniaxial nature. Resistance measurements on two kinds of organic conductors, α-(BEDT–TTF)2KHg(SCN)4 and α-(BEDT–TTF)2I3 under the uniaxial strain showed novel electric properties that have never been found under hydrostatic pressures. Their properties were found to be largely dominated by the direction of the uniaxial strain even when it is applied along directions in the conducting plane having a two-dimensional nature.

Crystal structure analysis under uniaxial strain at low temperature using a unique design of four-axis x-ray diffractometer with a fixed sample

For the purpose of crystal structure analysis under uniaxial strain at low temperatures, we developed a pressure cell for uniaxial compression and a unique design of an x-ray diffractometer wherein both the x-ray source and the detector are capable of two-axial rotation with a fixed sample. This arrangement is advantageous to crystal structure analyses under extreme conditions that require a large and heavy apparatus. Using the present diffractometer, we performed the crystal structure analyses of the organic conductor, α-(BEDT–TTF)2I3 (BEDT–TTF denotes bis(ethylene)dithio-tetrathiafulvalene), under uniaxial strain and ambient pressure, and at room and low temperatures, and obtained results that were qualitatively consistent with those of resistivity measurements.

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...

Electrical and Structural Properties of θ-type BEDT-TTF Organic Conductors under Uniaxial Strain

In order to investigate the relationships between crystal structures and electronic properties of θ-type BEDT-TTF organic conductors, electrical properties of θ-(BEDT-TTF) 2 Ag(CN) 2 and θ-(BEDT-TTF) 2 CsZn(SCN) 4 and crystal structures of θ-(BEDT-TTF) 2 CsZn(SCN) 4 under uniaxial strain are investigated. The resistivity measurements for both salts under uniaxial strain show that the inter-columnar uniaxial strain preserves the metallic nature while the intra-columnar one induces an insulating behavior, which are reminiscent of the charge-ordered state of θ-(BEDT-TTF) 2 RbZn(SCN) 4 . Structure analyses of θ-(BEDT-TTF) 2 CsZn(SCN) 4 under uniaxial strain indicate that the inter-columnar strain slightly increases the diagonal transfer integral but does not vary the vertical one, and the intra-columnar uniaxial strain largely increases the vertical transfer integral but does not change the diagonal one. Based on these experimental results, the key parameters to determine the electrical properties of θ-type B...

Crystal and Electronic Structures of the Quasi-Two-Dimensional Organic Conductor α-(BEDT-TTF)2I3 and Its Selenium Analogue α-(BEDT-TSeF)2I3 under Hydrostatic Pressure at Room Temperature

We perform crystal structure analyses of the organic conductor α-(BEDT-TTF) 2 I 3 [where BEDT-TTF denotes bis(ethylene)dithiotetrathiafulvalene] and its selenium analogue α-(BEDT-TSeF) 2 I 3 [where BEDT-TSeF denotes bis(ethylene)dithiotetraselenafulvalene] at room temperature under hydrostatic pressure, where they are expected to have zero-gap points at the Fermi level with a Dirac-cone-type dispersion for a massless particle. We calculate the electronic band structures using a combination of the extended Huckel molecular orbital calculation based on the obtained crystal structures and the tight-binding band structure calculation. We find that I) the obtained Fermi surfaces of both salts under hydrostatic pressure are simply larger than those at ambient pressure owing to an increase in overlap integrals caused by the pressure, and II) electronic structures having zero-gap points with a Dirac-cone-type dispersion at the Fermi level are realized only in α-(BEDT-TTF) 2 I 3 by the introduction of suitable sit...

Superconductivity at 5.4 K in β-Bi2Pd

We investigate bulk superconductivity in a high-quality single crystal of Bi 2 Pd (β-Bi 2 Pd; space group: I 4/ m m m ) with a superconducting transition temperature of 5.4 K, by exploring its electrical resistivity, magnetic susceptibility, and specific heat. The temperature dependence of the electrical resistivity shows convex-upward behavior at temperatures greater than 40–50 K, which can be explained using a parallel-resistor model. In addition, the temperature dependences of the upper critical magnetic field and the specific heat suggest that β-Bi 2 Pd is a multiple-band/multiple-gap superconductor.We investigate bulk superconductivity in a high-quality single crystal of Bi

Semiclassical and non-classical angular effects of magnetoresistance in (TMTSF)2X

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Superconductivity at 5.4 K in

Pd (

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