| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1988: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1987: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
The main point of this proposal was in the search for new type or high-T_c superconductivity in oxide systems. It was actually discovered by Bednorz and Muller after the proposal had been made. Therefore, we were ready to begin the study on the high-T_c oxides immediately after their discovery. Moreover, because the head investigator of this project could also join the research groups of other larger projects (1987, 1988-1990), we could strongly develop the works using all of the financial supports: Both the search for new high-T_c oxides and study on various physical properties of the high-T_c oxides to elucidate the mechanism of the superconductivity have been carried out. Because we expected that the mechanism could be understood rather by the accumulation of various kinds of experimental results than by a small number of the excellent works, we studied from widely spread view points.
In each experiment, we chose the best samples for its purpose among sintered pellets and single crys
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tals. Transport, thermal and magnetic properties and other basic properties were studied here. The structure determinations were also done. Other various kinds of studies were carried out in collaboration with researchers in other groups. The obtained results have presented rather important information which can strongly restrict the possible mechanisms of the superconductivity. Examples of our main contributions are given below. (i) Single crystals of (La,M)_2CuO_4 (M=Ba and Sr) with superconducting transition was first prepared and the low dimensional conduction was observed, which indicated, as we stressed, that the role of CuO_2 plane was primarily important. (ii) The superconducting system with Tl was first found by us. (iii) The absence of the t-linear term in the low temperature specific heat was first experimentally proved, which presented the large restriction to the theoretical models of the superconductivity. (iv) Large single crystals were prepared and used in the neutron inelastic scattering experiments. The results gave the useful knowledge on the behaviors of the spin systems at the Cu atom sites. The two magnon Raman experiments on our crystals also gave the important information on the same subject. (v) The superlattice structure of Bi-Sr-Cu-O was determined by X-ray four circle diffraction. (vi) Anomalous behaviors of transport properties in (La,Ba)_2CuO_4 which are closely related to the anomalous Ba-concentration dependence of T_c were found and studied in detail. (vii) Through the study on the variation of the physical properties of (La,Sr)_2CuO_4 and (La,Sr)_2(Cu,Ni)O_4 the characteristic natures of the electronic systems of the high-T_c oxides were clearly demonstrated. (viii) Physical properties and oxygen isotope effect of (Ba,K)BiO_3 were studied and it was pointed out that the superconductivity in the system could be considered to be phonon-mediated. Less
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