Quasiparticle damping and the coherence peak in YBa2Cu3O7- delta

Tuning the resonance in high-temperature superconducting terahertz metamaterials

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 observe efficient metamaterial resonance switching and frequency tuning. The results are well reproduced by numerical simulations of metamaterial resonance using the experimentally measured complex conductivity of the superconducting film. We develop 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 predicts more efficient resonance tuning in metamaterials consisting of a thinner superconducting split-ring resonator array, which are also verified in subsequent experiments.

Large dynamic resonance transition between surface plasmon and localized surface plasmon modes

We present resonant terahertz transmission in a composite plasmonic film comprised of an array of subwavelength metallic patches and semiconductor holes. A large dynamic transition between a dipolar localized surface plasmon mode and a surface plasmon resonance near 0.8 THz is observed under near infrared optical excitation. The reversal in transmission amplitude from a stop-band to a pass-band and up to pi/2 phase shift achieved in the composite plasmonic film make it promising in large dynamic phase modulation, optical changeover switching, and active terahertz plasmonics.

Optical properties of c-axis oriented superconducting MgB2 films

Temperature dependent optical conductivities and dc resistivity of c-axis oriented superconducting (T(c) = 39.6 K) MgB2 films (approximately 450 nm) have been measured. The normal state ab-plane optical conductivities can be described by the Drude model with a temperature independent Drude plasma frequency of omega(p,D) = 13 600+/-100 cm(-1) or 1.68+/-0.01 eV. The normal state resistivity is fitted by the Bloch-Grüneisen formula with an electron-phonon coupling constant lambda(tr) = 0.13+/-0.02. The optical conductivity spectra below T(c) of these films suggest that MgB2 is a multigap superconductor.