Nanoscale layering of antiferromagnetic and superconducting phases in   Rb2Fe4Se5
  We studied phase separation in a single-crystalline antiferromagnetic superconductor Rb2Fe4Se5 (RFS) using a combination of scattering-type scanning near-field optical microscopy (s-SNOM) and low-energy muon spin rotation (LE-\mu SR). We demonstrate that the antiferromagnetic and superconducting phases segregate into nanometer-thick layers perpendicular to the iron-selenide planes, while the characteristic in-plane size of the metallic domains reaches 10 \mu m. By means of LE-\mu SR we further show that in a 40-nm thick surface layer the ordered antiferromagnetic moment is drastically reduced, while the volume fraction of the paramagnetic phase is significantly enhanced over its bulk value. Self-organization into a quasiregular heterostructure indicates an intimate connection between the modulated superconducting and antiferromagnetic phases. 
A. Charnukha, A. Cvitkovic, T. Prokscha, D. Pr\"opper, N. Ocelic, A.   Suter, Z. Salman, E. Morenzoni, J. Deisenhofer, V. Ts...
cond-mat.supr-con cond-mat.str-el