| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2002: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2001: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
・Stripe order of high-Tc superconductor
The stripe model is a plausible one which can explain the so-called 1/8 problem, namely, the anomalous suppression of superconductivity in the La-based cuprate with the hole concentration per Cu p 〜 1/8. It has been proposed that the static order of holes and spins observed in the La-based cuprate from the neutron scattering experiment. If the stripe order is characteristic of the CuO_2 plane, it will exist not only in the La-based cuprate but also other high-Tc cuprates with p 〜 1/8. In this study, in order to search for the 1/8 anomaly in the Bi-based cuprate, we investigated the superconducting transition temperature Tc of Bi_2Sr_2Ca_<1-x>Y_x(Cu_<1-y>Zn_y)_2O_<8+δ> single crystals. The Zn substitution is due to the stripe-patterned static order pinned by Zn. We have succeeded in growing of much kinds of single crystal with 0【less than or equal】x【less than or equal】0.5, y = 0, 0.025 by floating-zone method, which were annealed in order to fix ex
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cess oxygen content σ . The x dependence of Tc defined as the onset temperature of the Meissner effect has appeared a local minimum of Tc at x〜0.35 for y = 0, 0.025. At present, Hall effect and thermoelectric power are being measured in order to examine the correlation of this local minimum and 1/8 problem.
Thermal conductivity of low-dimensional quantum spin system
We have looked for large thermal-conductivity due to magnons, κmagnon in various kinds of low-dimensional quantum spin systems, such as the two-leg spin-ladder system Sr_<14>Cu_<24>O_<41>, the two-dimensional spin-dimer system SrCu_2(BO_3)_2, the four-leg spin-ladder system La_2Cu_2O_5, the two-dimensional spin system Cu_3B_2O_6 and the one-dimensional spin system Ca_2Y_2Cu_5O_<10>, using large-sized single-crystals grown by the TSFZ method. Large κmagnon has been found in the spin-gap state of Sr_<14>Cu_<24>O_<41> whose band width of the triplet excitation is large, owing to the enhancement of the mean free path of magnons. In gapless systems, it has been found that κmagnon increases with increasing magnon-velocity, which increases with increasing exchange-interaction between Cu^<2+> spins and is larger in antiferromagnetic spin-correlation systems than in ferrromagnetic spin-correlation systems. Therefore, it is concluded that essential factors of large κmagnon are a large band-width of the triplet excitation in a spin-gap system, a large exchange-interaction and antiferromagnetic spin-correlation rather than ferromagnetic spin-correlation. Less
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