Critical current density and ac harmonic voltage generation in $YBa_2Cu_3O_{7-\delta}$ thin films by the screening technique

摘要

The temperature and field dependence of harmonics in voltage $V_n=V'_n-iV"_n$using the screening technique have been measured for$\mathrm{Y}\mathrm{Ba}_{2}\mathrm{Cu}_3\mathrm{O}_{7-\delta}$ superconductingthin films. Using the Sun model we obtained the curves for thetemperature-dependent critical current density $J_c(T)$. In addition, weapplied the criterion proposed by Acosta et al. to compute $J_c(T)$. Also, wemade used of the empirical law $J_c \propto (1-T/T_c)^n$ as an input in ourcalculations to reproduce experimental harmonic generation up to the fifthharmonic. We found that most models fit well the fundamental voltage but higherharmonics are poorly reproduced. Such behavior suggests the idea that higherharmonics contain information concerning complex processes like flux creep orthermally assisted flux flow.