  In this Letter we present resonance properties in terahertz metamaterials
consisting of a split-ring resonator array made from high temperature
superconducting films. By varying the temperature, we observed efficient
metamaterial resonance switching and frequency tuning with some features not
revealed before. The results were well reproduced by numerical simulations of
metamaterial resonance using the experimentally measured complex conductivity
of the superconducting film. We developed a theoretical model that explains the
tuning features, which takes into account the resistive resonance damping and
additional split-ring inductance contributed from both the real and imaginary
parts of the temperature-dependent complex conductivity. The theoretical model
further predicted more efficient resonance switching and frequency shifting in
metamaterials consisting of a thinner superconducting split-ring resonator
array, which were also verified in experiments.
