We measured the microwave surface impedance of FeSe0.4Te0.6 single crystals with and without external magnetic fields. The superfluid density exhibited a quadratic temperature dependence, indicating a strong pair-breaking effect. The flux-flow resistivity behaved as ρf(B<Bc2)/ρn=αB/Bc2. The observed α value of ≈0.66 was considerably smaller than that of other Fe-based materials (α≥1) and was attributed to a back-flow of superfluids remarkable in disordered superconductors. This is an observation of the back-flow phenomenon caused by an origin other than the vortex pinning in multiple-band systems.
|Physical Review B - Condensed Matter and Materials Physics
|Published - 2015 Feb 11