Measurements of the RF surface resistance of high-Tc superconductors

An experimental program is being conducted to assess the applicability of high-T_c superconductors for use in high-power RF and microwave devices. The program involves the measurement of the RF surface resistance of high-T_c samples at frequencies between 0.15 and 40 GHz and RF surface magnetic fields as high as 640 G. Polycrystalline samples were found to have surface resistances which increase monotonically with RF-field amplitude, saturating at high field at a few percent of the normal-state surface resistance just above T_c. The data indicate that for high-T _c materials at low-RF fields, sufficiently low surface resistances are achieved, but at high fields (e.g. ⩾30 G) the surface resistances are too large by a factor typically ~100