Anisotropic microwave absorption of Bi-Sr-Ca-Cu-O single crystals

We have measured the microwave absorption of Bi/sub 2.1/Sr/sub 1.6/CaCu2O/sub x/ single crystals as a function of the temperature T and the dc magnetic field H. A huge anisotropy, greater than 1000:1, is observed in the absorption, depending on the orientation of the microwave electric field relative to the c axis of the crystal. This result is consistent with the view that superconductivity in this compound may be quasi-two-dimensional. There is an additional, but much smaller, dependence on the orientation of an applied dc magnetic field