Interrogating the superconductor Ca(10)(Pt(4)As(8))(Fe(2−x)Pt(x)As(2))(5) Layer-by-layer

Ever since the discovery of high-T(c) 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 Ca(10)(Pt(4)As(8))(Fe(2)As(2))(5) provides opportunities to explore superconductivity layer by layer, because it contains both superconducting building blocks (Fe(2)As(2) layers) and intermediate Pt(4)As(8) layers. Cleaving a single crystal under ultra-high vacuum results in multiple terminations: an ordered Pt(4)As(8) layer, two reconstructed Ca layers on the top of a Pt(4)As(8) layer, and disordered Ca layer on the top of Fe(2)As(2) 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/Pt(4)As(8) layer. Our results indicate that an ordered structure with proper charge balance is required in order to preserve superconductivity.