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Register a new userDependence of the gap parameter on the number of CuO2 layers in a unit cell of optimally doped BSCCO, TBCCO, HBCCO and HSCCO
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We have measured the superconducting gap Ds in optimally doped samples of BSCCO, TBCCO, HBCCO and HSCCO by Andreev and tunnelling spectroscopy and by ARPES. We have found that the low-temperature value of the gap within experimental errors is linearly increasing with the number n of CuO2 layers in the unit cell of the investigated HTSC-families (n < 4)
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Using high-energy diffraction we show that a 4-unit-cell superstructure, q0=(1/4,0,0), along the shorter Cu-Cu bonds coexists with superconductivity in optimally doped YBCO. A complex set of anisotropic atomic displacements on neighboring CuO chain planes, BaO planes, and CuO2 planes, respectively, correlated over ~3-6 unit cells gives rise to diffuse superlattice peaks. Our observations are consistent with the presence of Ortho-IV nanodomains containing these displacements.
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Electronic heat transport in the normal state of a high-quality single crystal of optimally-doped superconductor YBa2Cu3O6.95 was studied by measurements of longitudinal and transverse transport coefficients. For the temperature range from 100 to 300 K, the Hall-Lorenz number (Lxy) depends weakly on temperature and is about two times larger than the Sommerfeld value of the Lorenz number Lo = (pi^2)/3. Our results can be interpreted using a Fermi liquid model when effects of the pseudogap that opens at the Fermi level are included. However, we find that the bipolaron model can also explain both the enhanced value and the weak temperature dependence of the Hall-Lorenz number.
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