Mototada Kobayashi

Susceptibility Fluctuation in Superconducting First Stage Potassium Graphite Intercalation Compound near Transition Temperature

The magnetic susceptibility of the first stage potassium graphite intercalation compound, of which the host graphite was grafoil sheets, was measured by the Hartshorn bridge method. The superconducting transition temperature of C 8.8 K was found to be 125 mK. The susceptibility fluctuation in the transition region was examined with Aslamazov-Larkins theory, and the dimensionality in the transition region gradually changed as temperature was decreased toward T c .

Potassium Concentration Dependence of the Superconductivity in the Potassium Graphite Intercalation Compounds

Magnetic susceptibilities have been measured at temperatures down to 60 mK by AC Hartshorn bridge method for the potassium graphite intercalation compounds with several compositions (C 8.0 K ∼C 21.6 K) prepared by the use of HOPG. T c is nearly constant to be ∼150 mK for C 8.0 K ∼C 14.7 K, while no transition is found down to 60 mK for C 16.7 K and C 21.6 K. As the K concentration is decreased, the superconducting characteristic changes from type II to type I for the magnetic field H parallel to the layers, while it maintains type I for H perpendicular to the layers. The superconducting fluctuation above T c , the effective mass ratio and the curvature of H c2 versus T curve are investigated; all of them lead to the result that 3D character increases with the decrease of the K concentration. The constancy of T c above the critical K concentration is also discussed.

Superconductivity in graphite–potassium intercalation compounds

Superconductivity transitions were studied in golden graphite−potassium compounds. The transition temperature changes were studied by adding hydrogen to the compound. (AIP)

Superconductivity in the Potassium Graphite Hydride C8KH0.19

The superconductivity in C 8 KH 0.19 (a hydride of the first stage potassium graphite intercalation compound) was observed in AC magnetic susceptibility measurements. The transition temperature T c is 220 mK. The superconducting characteristic is type I for the magnetic field H perpendicular to the layers and type II for H parallel to the layers. The temperature dependence of the critical fields is also investigated. These results are compared with those of the potassium graphite. T c enhancement by hydrogenation has been confirmed.

Transport and superconducting properties of potassium hydride graphite intercalation compounds

Abstract Potassium hydride graphite intercalation compounds were prepared by the direct intercalation of potassium hydride into HOPG and their structures were confirmed by (00l) X-ray diffraction. The resistivity of the stage-1 to -3 compounds were presented as a function of temperature. As a preliminary measurement of susceptibility, the diamagnetism attributed to superconductivity was detected in the stage-2 C8KHx, which increases continuously from 360mK down to 70mK.

Magnetic property of an organic conductor, (TTM-TTF) (I3)0.823

Abstract The magnetic property of an organic conductor, (TTM-TTF)(I 3 ) 0.823 , has been investigated by means of ESR measurement. An ESR spectrum consists of two signals; a sharp signal due to conduction electron spins on TTM-TTF molecules and a broad signal due to localized spins on iodine molecules. The spin susceptibility associated with the sharp signal shows a metal-insulator transition around 100 K. The strong temperature dependence of the g-value for the broad signal suggests the change in the electronic state of the iodine acceptor accompaning the phase transition.

Superconductivity in the first stage rubidium graphite intercalation compound C8Rb

Abstract The superconductivity in C8Rb has been observed in AC magnetic susceptibility and magnetization measurements with the magnetic field applied perpendicularly and parallel to the c-plane. The transition temperature Tc is found to be 26 mK. The superconducting properties are discussed in comparison with those of C8K.

Chemical and Physical Properties of Cation Radical Salts of BEDT-TTF

Abstract Extension of TTF skeleton by alkylthio groups makes the donors superior even to TMTSF concerning ionization potential, polarizabi1ity, and on-site Coulomb repulsion. Furthermore, due to the presence of the outer sulfur atoms, BEDT-TTF can form two-dimensional network by side-by-side arrangement in the complexes. The balance between the face-to-face and side-by-side interactions results in a variety of polymorphic complexes. We have been studying chemical, physical, structural, and designing works of cation radical salts of BEDT-TTF compounds. (BEDT-TTF) 2ClO4. (TCE).0.5 shows metallic character down to 1.4Kwith phase transitions at ca. 170K and 15K in electrical conductivity. The ESR and static magnetic studies show additional phase transitions. Different temperature dependence of magnetic properties was observed in the relaxed and quenched samples of this salt. A magnetic phase below 20K was formed by relaxing the salt at high temperature.

Superconducting transition in the first stage potassium graphite intercalation compounds

Abstract The real and imaginary parts of the magnetic susceptibility X ′ and X ″ were measured for potassium graphite intercalation compounds with various ratios of K to C content (C 8.0 K-C 9.4 K) prepared with HOPG. The transition temperature to the superconducting state, T c , was about 152 mK, and independent of K concentration. C 8.0 K and C 8.1 K were found to be of type 1 for H perpendicular to the c plane and of type 2 for H parallel to the c plane, while C 9.4 K was found to be of type 1 in both the directions of H. H c and H c2 decreased with the K concentration. H c and H c2 perpendicular to the c plane versus T curves had slightly positive curvatures in stoichiometric, and negative ones in less contained K compounds. The behaviour related to the dimensionality above T c is also discussed, taking into account the susceptibility fluctuation, and the two-dimensional behaviour was found at temperature very close to T c .

Responsible Layer for Superconductivity in the First Stage Potassium Graphite Intercalation Compound

The superconductivity in the first stage potassium graphite intercalation compound is discussed in connection with the electron transfer rate from potassium atom to graphite layers. From this discussion together with the experimental result that transition temperature T c depends little on the K atom concentration above a critical concentration, we conclude that the superconductivity takes place mainly on the graphite layer. The mechanism to increase three dimensional character with decreasing K atom concentration is also discussed.