Observation of mesoscopic phase separation in KxFeySe2 by scanning microwave microscopy

Abstract We investigated the local electric property of iron-based superconductor K x Fe y Se 2 ( x = 0.8 , y = 1.6 – 2 , T c = 31 K ) using scanning tunneling/microwave microscope. The characteristic pattern originating from mesoscopic phase separation of the metallic and the semiconducting phase was observed. From the comparison with previously reported SEM/EDS results, we identified the metallic phase and the semiconducting phase as the minor Fe-rich phase and the major K 2 Fe 4 Se 5 phase, respectively.