Structure in the magnetic-field-dependent microwave absorption of Bi-Sr-Ca-Cu-O single crystals

We have observed structure in the magnetic field dependence of the microwave absorption of Bi/sub 2.1/Sr/sub 1.6/CaCu2O/sub x/ single crystals below the superconducting transition temperature. An absorption peak is observed at low fields, and the peak position and width have strong temperature and angular dependences. Two peaks can be resolved in some samples. Hysteresis in the low-field absorption peak indicates extremely anisotropic flux trapping in these crystals for T<25 K. Flux parallel to the c axis of the crystal is almost completely trapped, whereas flux normal to c is only weakly trapped