Fyzikální ústav Akademie věd ČR

By combining the unique infrared imaging capabilities and nanoscale resolution of the scattering-type scanning near-field optical microscopy (s-SNOM) with bulk sensitivity at variable depth of low-energy muon spin rotation (LE-mSR) we determined the geometry and magnitude of the phase separation in nearly-stoichiometric superconducting Rb2Fe4Se5 single crystals with Tc = 32 K [1]. The paramagnetic domains were found to have a shape of thin metallic sheets parallel to the iron-selenide plane with a characteristic size of only several nanometers out of plane but up to 10 μm in plane.