The surface impedance of type II superconductors in the mixed state

Using a quarter wave coaxial resonator containing the superconducting sample as the center element, the resistive and reactive components of the surface impedance have been measured on niobium over the entire static H-field range of the mixed state at frequencies between 70 MHz and 930 MHz. The samples included one in the plastically deformed condition and one which had been annealed at 1800°C for 2 hours in a vacuum of 7 × 10^-8torr; both had about the same resistivity ratio (∼14). The two samples differed considerably in the ratio of the resistive to reactive component of the surface impedance. The phenomena is believed to be a consequence of the nature of the electronic excitations characterizing the fluxiod cores.