Anisotropy of nonlinear properties of Bi2Sr2CaCu2O8 crystals in a magneticfield

The nonlinear response of a high-temperature superconductor to an external ac magnetic field has been studied experimentally as a function of sample o rientation relative to ac and de external magnetic fields. The even harmoni cs of the response vanish in the case of a ceramic sample if the de magneti c field is perpendicular to the ac field. This is not the case for a crysta lline Bi2Sr2CaCu2O8 sample where the amplitudes of even harmonics vary peri odically with a sample rotated about the ac field. To explain this effect, a theoretical model taking into account the sample crystal structure is pro posed.