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Magnetic anisotropy of some cuprate superconductors

We report magnetic anisotropy data obtained using cantilever torque or Squid magnetom- etry, for single crystals of YBa2Cu4O8, YBa2Cu3O6+x ; La2¡xSrxCuO4 and Bi2Sr2CaCu2O8¡x, grown by several di®erent groups. At present the main results are: (1) The anisotropy far above Tc is dominated by anisotropy in the spin susceptibility. By comparing data for YBa2Cu4O8and YBa2Cu3O7we show that the T-dependence is caused by the pseudogap. (2) At lower T, analysis in terms of weak, quasi- 2D, Gaussian superconducting °uctuations gives values of the in-plane superconducting coherence length, and hence independent estimates of the Nernst coe±cient above Tc. (3) Data for the ¯eld dependence of the °uctuations nearer Tc are used to look for deviations from the above Gaussian picture. (4) There is some evidence from the magnetic suscep- tibility, Knight shift, susceptibility anisotropy and heat capacity, that the small pockets of carriers detected in high ¯eld quantum oscillation experiments on YBa2Cu4O8andYBa2Cu3O6+x are still present at low ¯elds. X Prefer Oral Session Pr

High-Tc superconductors; Nernst effect; Superconducting fluctuations; Pseudogap

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