Fundamental and harmonic AC responses to dierent annealing rates of Bi2Sr2CaCu2O8 single crystals
نویسندگان
چکیده
Three Bi2Sr2CaCu2O8 single crystals with dierent annealing processes have been measured in terms of complex AC susceptibilities vn vn ÿ iv00 n (n 1; 3) to reveal the eect of ̄ux-pinning strength. The third harmonic susceptibility changes dramatically when the pinning strengths are dierent due to dierent annealing processes, although the fundamental susceptibilities are quite similar. The experimental data are explained by the calculations based on ®nite thickness type-II superconductors in the presence of a geometric barrier. It has been found that the temperature dependence of the third harmonic susceptibility of the crystals follows the model predictions. When the sample is slowly cooled, the geometric barrier plays a signi®cant role in the third harmonic AC susceptibility. Its eect is suppressed when the single crystals are cooled rapidly from high temperature. Ó 2001 Elsevier Science B.V. All rights reserved.
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