1999 Fiscal Year Final Research Report Summary
The flux motion and the symmetry of the Cooper pairs in a high-Tc superconductors
| Project/Area Number |
09450003
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied materials science/Crystal engineering
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
NOJI Takashi Graduate School of Engineering, Tohoku University, Assistant Researcher, 大学院・工学研究科, 助手 (50180740)
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| Co-Investigator(Kenkyū-buntansha) |
KOIKE Yoji Graduate School of Engineering, Tohoku University, Professor, 大学院・工学研究科, 教授 (70134038)
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| Project Period (FY) |
1997 – 1999
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| Keywords | high-Tc superconductor / single crystal / TSFZ method / untwined / ladder system / thermal conductivity |
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| Research Abstract |
Single crystals of the representative high-Tc superconductor YBaィイD22ィエD2CuィイD23ィエD2OィイD27ィエD2 are usually twinned. The twin boundaries prevent us from studying the intrinsic physical properties of the material. On the other hand, it is known that (Ca,La,Ba)ィイD23ィエD2CuィイD23ィエD2OィイD2yィエD2(CLBCO) and NdBaSrCuィイD23ィエD2OィイD2yィエD2(NBSCO) among the 1-2-3 type superconductors are tetragonal in the crystal structure. Therefore, superconducting single-crystals of these compounds must be twin-free. We tried the single-crystal growth of CLBCO and NBSCO by the travelling-solvent floating zone method to obtain originally twin-free single-crystals of the 1-2-3 type superconductors. Trying various kinds of solvent, we have succeeded in obtaining single crystals with the dimensions of the order of 1×1×0.5mmィイD113ィエD1. As-grown single-crystals of CLBCO and NBSCO are tetragonal and non-superconducting. Through the annealing in oxygen, single crystals of CLBCO have became superconductors with Tc=55 - 65
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K, keeping the tetragonal structure. On the other hand, single crystals of NBSCO have changed from tetragonal to orthorhombic through the annealing in oxygen, though they have become superconductor with Tc = 55 K.
Spin gap of SrィイD214ィエD2CuィイD224ィエD2OィイD241ィエD2 studied by the thermal conductivity.
The layered cuprate SrィイD214ィエD2CuィイD224ィエD2OィイD241ィエD2 consisting of two-dimensional CuィイD22ィエD2OィイD23ィエD2 ladder planes (regarded as a spin-1/2 ladder system with two legs) and one-dimensional CuOィイD22ィエD2 chains. The carrier-doped spin ladder systems SrィイD214-xィエD2AィイD2xィエD2CuィイD224ィエD2OィイD241ィエD2 (A=Ca,La) have attracted great interest, triggered by the theoretical prediction on the spin gap and superconductivity. We have investigated the spin gap and the hole pairing in the ladder from the thermal conductivity measurement and found two kinds of spin excitation as predicted theoretically. The observed thermal conductivity κ has been analyzed to be composed of κィイD2phィエD2, κィイD2spinィエD2 and κィイD2holeィエD2 due to phonons, spins and holes, respectively. The spin gap in the ladder estimated from κィイD2spinィエD2 is 〜400K and independent of x(Ca). This is regarded as corresponding to the excitation from spin-singlet to spin-triplet, as those estimate from the neutron scattering. The spin gap estimated from κィイD2holeィエD2 decreases with increasing x(Ca). This is regarded as corresponding to the dissociation of spin-singlet pairs, namely, the dissociation of hole pairs, as those estimate from the NMR measurements. Less
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