This commentary notes give brief discussion on material properties of high temperature superconductors from the aspect of suitability to the field effect device application and on principle concerning the modulation of superconductivity. Some examples of the drain current modulation in the test devices, YBCO-MISFETs, are shown. However, the actual data taken from the MISFETs are far from the goal. The major cause for this is arising from the degraded interface between YBCO channel layer and gate insulator. First measurement of the interfacial diffusion was carried out and some favorable combination of the gate insulator and YBCO channel is proposed.
Recent progress in the synthesis and the study on superconducting properties of Hg-based cuprates superconductors, HgBa2Ca(n-1)CunO2+2n+δ, is reviewed. An encapsulation and singlefiring (ECSF) technique is successfully utilized for the preparation of nearly single-phase samples of the Hg-based cuprates superconductors. Superconducting transition temperature, Tcmag, is enhanced to a record high value of -136K for a nearly single-phase Hg-1223 (n=3) sample. Physical properties, e.g.Tc, Jc and Hc, of the Hg-12 (n-1)n superconductors are compared with those of other known cuprate superconductors.
Superconducting coil has been developed for various types of demand. Especially for nuclear fusion application, we need very high magnetic field and hence large coil. For the purpose of applying it, it is very important to know the detail of the deformation of the conductor to make an exact control of the magnetic field. Mito made some tests on a small superconducting helical coil (11th International Conference on Magnet Technology (1989) 783). The coil we work in this time is solenoid type and has the same cross section, number of layers and winding curve as Mito's helical one. We investigated more detailed strain behavior and compared the data of solenoid with that of helical coil, and found that the shape of helical gave larger strain in windings. Thus we see the much dependence of the strain value on the winding type. By the way, some parts of a coil showed an irregular behavior in spite of the axisymmetric electromagnet force. Such behavior is specific to the each coil, because the coil seemed to have its own initial imperfection or load record during fabrication. This is result of small solenoid coil. But, in practice, to excite very large and complicated shape coil, we have to give more attention to initial imperfection or load history.