Microwave study of the critical state in high-T_c superconductors

The signals obtained from microwave absorption at the surface of high-Tc superconducting oxides in a magnetic field depend sensitivily on the amplitude of the magnetic-field modulation and the sign of the field sweep. They are insensitive to the modulation frequency and the rate of the field sweep. These effects are shown to have their origin in the properties of the superconducting critical state with pinning and depinning of fluxons during a modulation cycle. © 1988.