Microwave response of high-T c superconducting crystals: Results, problems, and prospects

The results of studying temperature behavior of the microwave surface impedance Z s (T) and conductivity tensor σ (T) (T) of high-T c superconducting (HTSC) single crystals are analyzed. The emphasis is on the experimental facts that are inconsistent with the known electrodynamic concepts of conductivity mechanisms in these materials. Possible reasons for the inconsistency are discussed in the context of structural features of the HTSC crystals, and the outlook for future investigations is outlined.