PHENOMENOLOGICAL DESCRIPTION OF THE MICROWAVE SURFACE IMPEDANCE AND COMPLEX CONDUCTIVITY OF HIGH-T_c SINGLE CRYSTALS
Trunin M.R., Nefyodov Yu.A., Herman J.Fink

Received: April 4, 2000

PACS: 74.25.Nf, 74.72.-h, 74.20.De, 74.25.Fy

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Measurements of the microwave surface impedance Z_s(T)=R_s(T)+iX_s(T) and of the complex conductivity σ_s(T) in the ab-plane of high quality high-T_c YBCO, BSCCO, TBCCO, and TBCO single crystals are analyzed. Experimental data of Z_s(T) and σ_s(T) are compared with calculations based on a modified two-fluid model that includes a temperature-dependent quasiparticle scattering and a unique temperature variation of the density of superconducting carriers. We elucidate agreement as well as disagreement of our analysis with the salient features of the experimental data. We review the existing microscopic models based on unconventional symmetry types of the order parameter and on novel quasiparticle relaxation mechanisms.