Spin-glass phase microwave study in high-T_C superconductors

Measurement of low-field microwave absorption in single-crystal YBa2Cu3O7-δ shows a series of equally spaced, narrow, anisotropic absorption lines. With the external magnetic field parallel to the twin planes, a typical line spacing is about 200 mOe with a linewidth of about 2 mOe. These lines are associated with the motion of fluxons into the regular array of twin planes. The widely observed absorption in the ceramic is therefore a powder spectrum of many small crystallites with similar line spectra, which are unresolved. © 1988.