On the causes of low critical current in twin film high-temperature superconductors

The influence of internal local and external demagnetization fields on the critical current density of inter-doublet Josephson weak bonds Jc of high-temperature superconducting YBCO samples is investigated using the oscillation differential technique of local approximation. In the zero-field and zero-field cooling with flux accumulation regimes for samples with different Jc and twin sizes d, the demagnetization fields of samples HD1 and HD2 have been measured. The values of: d; thermodynamic first critical magnetic fields of twins Hic1; twin demagnetization fields HD tr; density of intra-twin effective critical currents Jc ef; critical pinning currents Jc p and shielding Meissner critical currents Jc M are determined. It is shown that at Hic1 fields the twins of large sizes “disintegrate” into a group of smaller twins with close demagnetizing factors. It is found that an increase in Jc M, Jc ef, and a decrease in d lead, on the one hand, to a decrease in Jc due to an increase in the demagnetization field of the sample HD and HD tr created by Jc ef and Jc M, and, on the other hand, to an increase in Jc ef and Jc M due to a decrease in d.