  Ever since the discovery of high-Tc superconductivity in layered cuprates,
the roles that individual layers play have been debated, due to difficulty in
layer-by-layer characterization. While there is similar challenge in many
Fe-based layered superconductors, the newly-discovered Ca10(Pt4As8)(Fe2As2)5
provides opportunities to explore superconductivity layer by layer, because it
contains both superconducting building blocks (Fe2As2 layers) and intermediate
Pt4As8 layers. Cleaving a single crystal under ultra-high vacuum results in
multiple terminations: an ordered Pt4As8 layer, two reconstructed Ca layers on
the top of a Pt4As8 layer, and disordered Ca layer on the top of Fe2As2 layer.
The electronic properties of individual layers are studied using scanning
tunneling microscopy/spectroscopy (STM/S), which reveals different spectra for
each surface. Remarkably superconducting coherence peaks are seen only on the
ordered Ca/Pt4As8 layer. Our results indicate that an ordered structure with
proper charge balance is required in order to preserve superconductivity.
