Microwave Studies on FeSe Superconductors.
A particularly interesting compound among the family of Fe-based superconductors is FeSe which possesses several advantageous features for measuring and elucidating its superconducting properties. The microwave electrodynamic properties of stoichiometric FeSe were measured by a cavity perturbation technique based on a 940 MHz loop-gap resonator. Measurements surprisingly show that c-axis surface resistance and conductivity exhibit qualitatively similar behavior with those observed in the ab-plane at the superconducting state. This result implies that the charge transfer between FeSe-planes is enhanced by the development of long transport quasiparticle lifetimes below Tc.