Evaluation of crystallographic and electromagnetic defects in the superconducting crystals and films by analysis of magneto-microwave response

Magnetic-flux trapping in crystals and films of high-T-c superconductors is investigated from the microwave (MW) response detected by electron spin re sonance (ESR) spectrometer. For Bi2212 single crystals, the periodic MW spe ctra were observed at external magnetic fluxes Phi(X) = (k +/- 1/2)Phi(0); where k is an integer, along with the surface impedance signal. The periodi c spectrum is a clear evidence for the stepwise transitions (k->k+1) betwee n the energy states of Josephson-junction (JJ) links by MW absorption, whic h follows the stepwise penetration of quantized flux Phi(0),. Their analysi s provided information on the phase shift Delta phi = 0 or pi of the vortex current along the link in addition to the link size, link-surface orientat ion, and the number of the penetrated quanta. The YBCO epitaxial films, whi ch were fabricated by pulsed laser ablation-deposition (PLD), showed the th ree kinds of MW responses or their superimposed spectra: (1) surface impeda nce, (2) periodic spectra due to intra-crystal JJ, and (3) a complex spectr um characteristic of the flux dynamics at inter-granular JJ defects. They a re discussed in comparison with the film-crystallinity studied by X-ray dif fraction and scanning electron microscope (SEM) and have made it possible t o evaluate the degree of epitaxy and the defects that work as flux-trapping sites. (C) 2000 Elsevier Science B.V. All rights reserved.