By using magnetic sweeping method, the temperature and magnetic field dependencies of the experimental current density and the normalized relaxation rate have been obtained. The true critical current density correspon...By using magnetic sweeping method, the temperature and magnetic field dependencies of the experimental current density and the normalized relaxation rate have been obtained. The true critical current density corresponding to the zero activation energy has been carried out based on the collective-pinning and the thermally-activated flux motion models, and therefore the influences of the quantum tunneling effect and the thermal activation effect on the experimental critical current density are distinguished. It is found that, with temperature lower than 10 K, the relaxation rate will not drop to zero when T approaches zero K because of the occurrence of the flux quantum tunneling. This additional flux motion further reduces the experimental critical current density j making it saturated with lowering temperature.展开更多
In high Tc YBa2Cu3O7(Y123) superconductors, by substituting Y with some rare earth elements RE, a stress field surrounding these dopants will be generated due to the lattice mismatch. Based on the effective defect mod...In high Tc YBa2Cu3O7(Y123) superconductors, by substituting Y with some rare earth elements RE, a stress field surrounding these dopants will be generated due to the lattice mismatch. Based on the effective defect model, the interaction energy and the maximum elementary interaction force (/? between a fluxoid and a stress center are calculated. It is shown that the calculated values for fp can well interpret the data of the enhancement of measured critical current density j's for the substitution of Y with different rare earth elements. Furthermore, by substituting the Gd with Y in the GdBa2Cu3O7_s thin films, the measured critical current density (js) is increased, while the relaxation rate (S) is clearly lowered, which can be attributed to the presence of extra pinning centers. The temperature dependence of the true critical current density jc(T) and the pinning potential UC(T) were determined from the experiment data for both the pure and the substituted thin films. It is found that the experiment results for the pure film are close to the predictions of -pinning model, while those for the substituted thin film follow the theoretical expressions derived from the single vortex collective pinning model with the small size stress-field pinning centers, which strongly supports the idea that the enhancement of j, by the substitution resulted from the stress induced flux pinning rather than the magnetic pinning.展开更多
基金Project supported by the K.C. Wong Education Fund.
文摘By using magnetic sweeping method, the temperature and magnetic field dependencies of the experimental current density and the normalized relaxation rate have been obtained. The true critical current density corresponding to the zero activation energy has been carried out based on the collective-pinning and the thermally-activated flux motion models, and therefore the influences of the quantum tunneling effect and the thermal activation effect on the experimental critical current density are distinguished. It is found that, with temperature lower than 10 K, the relaxation rate will not drop to zero when T approaches zero K because of the occurrence of the flux quantum tunneling. This additional flux motion further reduces the experimental critical current density j making it saturated with lowering temperature.
基金Project supported by the Education Foundation of the Chinese National Education Commission and the National Center for R and D on Superconductivity.
文摘In high Tc YBa2Cu3O7(Y123) superconductors, by substituting Y with some rare earth elements RE, a stress field surrounding these dopants will be generated due to the lattice mismatch. Based on the effective defect model, the interaction energy and the maximum elementary interaction force (/? between a fluxoid and a stress center are calculated. It is shown that the calculated values for fp can well interpret the data of the enhancement of measured critical current density j's for the substitution of Y with different rare earth elements. Furthermore, by substituting the Gd with Y in the GdBa2Cu3O7_s thin films, the measured critical current density (js) is increased, while the relaxation rate (S) is clearly lowered, which can be attributed to the presence of extra pinning centers. The temperature dependence of the true critical current density jc(T) and the pinning potential UC(T) were determined from the experiment data for both the pure and the substituted thin films. It is found that the experiment results for the pure film are close to the predictions of -pinning model, while those for the substituted thin film follow the theoretical expressions derived from the single vortex collective pinning model with the small size stress-field pinning centers, which strongly supports the idea that the enhancement of j, by the substitution resulted from the stress induced flux pinning rather than the magnetic pinning.
