Electrical properties of one-dimentional Pt complexes and TCNQ salts are discussed in connection with the exciton mechanism of high temperature superconductivity proposed by Little. Bis (dimethylglyoximato) Pt (II) (Pt(DMG)2) and its related complexes exhibit a remarkable decrease in electrical resistance at high pressures. The least resistivity and the activation energy observed for Pt(DMG)2 are 10-1Ωcm and 0.005eV, respectively. These low values are tentatively attributed to the effect of hyperconjugation of methyl substituent on the electronic polarizability in the ligand. Magnitudes of electrical conductivities of TCNQ salts depend strongly on the nature of the cation. LeBlanc has suggested that the electronic polarizability of the cation is a more important determinant of the variation in conductivities. However, Torrance et al have showed that Coulomb interaction are strong in all TCNQ salts and that there is no evidence for excitonic screening. From the crystal and electronic structures, and electrical behavior at high pressure for TCNQ salts, we believe that the excitonic screening is not dominant for electrical properties of TCNQ salts.
A four-layer pancake coil, which has an inside diameter of 20mm, an outside diameter of 100mm, a hight of 24.8mm and a maximum field of 6.5T, is wound by a Nb3Sn tape (5mm wide and 0.155mm thick). The coil is force-cooled by a helium flow (liquid phase flow, two phase flow or supercritical flow) which passes radially through the layers from innermost turns to outside turns. The coil is energized and performance is investigated under each cooling condition. The experimental results show critical currents of the coil depend on sweep speeds of energizing current. The dependency for each condition is qualitatively explained by heat transfer q-ΔT curve of helium. It is revealed that, if the heat transfer rate and the cooling capability of supercritical helium is raised by increasing the flow rate, the coil has a possibility to show a better performance than it is immersed in liquid helium.
The previously reported experimental machine for the investigation of basic characteristics of MHD rotating machine with 8-shaped superconducting rotor-winding installed was improved in the following two points; 1) Axial length of the magnet and total turns of the winding were increased, 2) Stainless steel cylinder substituted for liquid metal MHD fluid was replaced by aluminum one. Electromagnetic forces on the metal cylinder were measured under the influence of the skin effect in high magnetic Reynolds number, and the results were compared with theoretical estimations.