Phenomenological description of the microwave surface impedance and complex conductivity of high-$T_c$ single crystals

TL;DR

This paper analyzes microwave surface impedance and complex conductivity in high-$T_c$ superconductors, comparing experimental data with a modified two-fluid model to understand quasiparticle dynamics and superconducting carrier behavior.

Contribution

It introduces a modified two-fluid model incorporating temperature-dependent quasiparticle scattering and carrier density variations, providing a phenomenological description of high-$T_c$ superconductor properties.

Findings

Good agreement with experimental $Z_s(T)$ and $\sigma_s(T)$ data.

Identifies discrepancies highlighting limitations of current models.

Reviews microscopic theories based on unconventional order parameters.

Abstract

Measurements of the microwave surface impedance $Z_s(T)=R_s(T)+iX_s(T)$ and of the complex conductivity $\sigma_s(T)$ of high-quality, high-$T_c$ single crystals of YBCO, BSCCO, TBCCO, and TBCO are analyzed. Experimental data of $Z_s(T)$ and $\sigma_s(T)$ are compared with calculations based on a modified two-fluid model which includes 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. Existing microscopic models are reviewed which are based on unconventional symmetry types of the order parameter and on novel mechanisms of quasiparticle relaxation.