STM/STS study of superconducting properties in Ca$_{10}$(Pt$_{4}$As$_{8}$)(Fe$_{2}$As$_{2}$)$_{5}$*

Newly discovered iron-based superconductor, Ca$_{10}$(Pt$_{4}$As$_{8}$)(Fe$_{2}$As$_{2}$)$_{5}$ (T$_{c}$ = 34 K) is studied using scanning tunneling microscopy/spectroscopy (STM/S). Given the symmetry of the crystal structure, several surface terminations are expected with roughly same probability: 1) Ca or partial Ca layer on top Fe$_{2}$As$_{2}$; 2) Ca or partial Ca layer on top Pt$_{4}$As$_{8}$ layer; 3) A Fe$_{2}$As$_{2}$ layer, and; 4) A Pt$_{4}$As$_{8}$ layer. Surprisingly, Fe$_{2}$As$_{2}$ related layers (1 \& 3) are rarely observed (less than 1\%). Instead, we observe Pt$_{4}$As$_{8}$ layers separated by unit-cell-high ($\sim$ 1 nm) steps accompanied with Ca or partial Ca layer on top Pt$_{4}$As$_{8}$ layer (1 - 2 {\AA} step height). Scanning tunneling spectroscopy reveals different spectra for each surface, with superconducting coherence peaks seen only on Ca layers. We argue that intermediary layers are proximity-coupled to superconducting Fe$_{2}$As$_{2}$ layers. The results from Ca$_{10}$(Pt$_{4}$As$_{8}$)(Fe$_{2}$As$_{2}$)$_{5}$ are discussed with the properties observed in other iron-based superconductors.