Kitomi Tsutsumi

Superconductivity in the layered compound 2H-TaS2

Abstract The layered compound 2H-TaS 2 is one of the typical materials which lead to charge density waves. However, much less information is available on the superconducting properties of this compound. The Meissner effect in 2H-TaS 2 was studied systematically with special emphasis on low-d.c. applied fields. The susceptibility χ = M / H is quite weak and the value of χ is less than −8.0 × 10 −3 emu cm −3 above 0.4 K, at least 10 times smaller than the magnitude for perfect diamagnetism. A transition occurs over a rather wide temperature range. An indication of diamagnetism appears around 1.5 K which is much higher than the value of 0.8 K reported as the transition temperature in the earlier literature. The magnetization curves depart from linearity at fields less than 2.0 Oe at 0.4 K, which implies that the lower critical field H cl of 2H-TaS 2 is extremely small.

Superconductivity in the metallic layered compound NbTe2

Abstract The layered-structure compound NbTe2 is one of the typical materials which lead to charge-density waves. However, much less information is available on the superconducting properties of this compound. Electrical resistivity and diamagnetic susceptibility have been measured for high-quality single crystals of NbTe2. The superconducting transition is observed at Tc of 0.5 K. The transition to the superconducting state depends strongly on the current density. Susceptibility χ ∥ = M H with applied magnetic fields parallel to the two-dimensional layers in the crystal is weak and the value of χ∥ is two times smaller than the magnitude for perfect diamagnetism in a magnetic field of 0.50 Oe. The susceptibility changes with external field, even less than 0.50 Oe at 0.40 K, which implies that the lower critical field Hc1 of NbTe2 is extremely small ( H c1

Electrical properties of lithium doped Nb3Te4

= 0.5 Oe ). The experimental results of NbTe2 are compared with the data of the other layered compound 2H-TaS2.

Superconductivity in a layered transition-metal dichalcogenide 2H-TaS2

Abstract The resistivity and the thermopower of Li doped Nb 3 Te 4 were measured from 1.4 to 300 K. The superconducting upper critical field was also measured. With addition of Li, the resistive anomaly at about 100 K decreases, while that at about 40 K increases. With the increase of Li concentration, the magnitude of the thermopower at about 100 K becomes smaller. These results are discussed in terms of the modification of the shape of the Fermi surfaces.

The Meissner effect in the layered superconductor 2HTaS2

Abstract We have investigated the superconductivity transition in a layered transition-metal dichalcogenide 2H-TaS2 by means of measuring electrical resistance down to 10 mK. We observed one which is highly sensitive to the current for the measurement of the electrical resistance. In addition the current-dependent-electrical resistance is clearly observed at 1.4 and 4.2 K respectively. This current-dependency is for the first time reported on this material. The physical origin is discussed in terms of the distribution of the superconductivity tansition temperature within the specimen.

Superconductivity in layered—structure compound NbTe2

Abstract The Meissner effect of the layered superconductor 2HTaS2 is studied by using an rf-SQUID magnetometer. Diamagnetic susceptibility χ|;=M/H in magnetic fields parallel to the layers is much less than −8.0 × 10−3 emu/cm3 at 0.40 K. A transition occurs over a quite wide temperature range. Magnetization curves depart from linearity at the field less than 2.0 Oe with increasing the field.

An evidence of the structural transformation at 150mk in ho-elpasolite observed by sr x-ray topography

Abstract Electrical resistivity and diamagnetic susceptibility have been measured for high-quality single crystals of NbTe2. The superconducting transition is observed at Tc of 0.5 K. The transition to the superconducting state depends strongly on the current density. Susceptibility χ∥ = M/H with applied magnetic fields parallel to layers in crystal is weak and the value of χ∥ is two times smaller than the magnitude for perfect diamagnetism in a magnetic field of 0.5 Oe.

Superconducting glass state in binary alloy Ti0.5V0.5 single crystal

In order to confirm a weak structural transformation in Cs22NaHoCl6 at 150mK of the transition temperature, some topographs above and below 150mK were taken by means of SR X-rays. Changes of the crystal texture observed from comparison of the topographic patterns in the Laue spots 513 and 315 indicate an occurrence of the structural transformation. After cooling down to the base temperature 14.5mK, temperatures of the specimen were raised up to 182.3mK above the transition temperature, but the crystal does not show any change to return to the crystal structure of the high temperature phase. Then, this transition is the first kind, suggested from the measurement of Schottky type specific heat with the long tail up to about 1K.

Superconductivity in noble-metal compound CoSi2

We report the results of the specific heat measurements at low-temperatures of the binary alloy Ti0.5V0.5 single crystal which undergoes the superconducting transition at 7.20 K. The single crystal of Ti0.5V0.5 is not only one of the strong-coupling superconductors but also a dirty type-II superconductor above about 2 K. However, this material exhibits anomalous behaviors in the specific heat below about 2 K. We attribute this anomalous behavior to the transition from the superconducting state into a superconducting glass state around about 2 K.

Low-temperature specific heat of Ti0.5V0.5 single crystal

Abstract We report the results of the electrical resistivity and the low-temperature specific heat measurements of CoSi2 single crystals in the normal metallic state and superconducting regime. The results show that CoSi2 is truly a noble-metal compound as suggested by photoemission experiments and band-structure calculations. A significant point is that the superconductivity of this noble-metal compound can be described by the BCS theory.