On Some Unsolved Problems in Microwav Uncoventional Superconductivity: from Authors’ Research Experience

The authors discuss a number of the unsolved problems and unexplained facts when the authors conducted relevant studies in the field of microwave superconductivity, namely in the field of surface impedance and complex conductivity of unusual superconductors. Here they considered the most important issues and facts, namely: i) microwave residual resistance; ii) temperature dependence of quasiparticle conductivity; iii) quasiparticle scattering collapse; iv) inequality of surface resistance and surface reactance at T ≥ T
_c
, v) unusual microwave response of resonant cavity near T
_c
depending of thin superconducting FeSeTe film orientation relative to microwave field.