Orbital selectivity of layer resolved tunneling on iron superconductor   Ba0.6K0.4Fe2As2
  We use scanning tunneling microscopy/spectroscopy (STM/S) to elucidate the Cooper pairing of the iron pnictide superconductor Ba0.6K0.4Fe2As2. By a cold-cleaving technique, we obtain atomically resolved termination surfaces with different layer identities. Remarkably, we observe that the low-energy tunneling spectrum related to superconductivity has an unprecedented dependence on the layer-identity. By cross-referencing with the angle-revolved photoemission results and the tunneling data of LiFeAs, we find that tunneling on each termination surface probes superconductivity through selecting distinct Fe-3d orbitals. These findings imply the real-space orbital features of the Cooper pairing in the iron pnictide superconductors, and propose a new and general concept that, for complex multi-orbital material, tunneling on different terminating layers can feature orbital selectivity. 
J.-X. Yin, X. -X. Wu, Jian Li, Zheng Wu, J.-H. Wang, C.-S. Ting, P.-H.   Hor, X. J. Liang, C. L. Zhang, P. C. Dai, X. C. Wan...
cond-mat.supr-con