Interrogating the superconductor Ca10(Pt4As8)(Fe2-xPtxAs2)5 Layer-by-layer

TL;DR

This study uses STM/S to analyze individual layers of the layered superconductor Ca10(Pt4As8)(Fe2-xPtxAs2)5, revealing that superconductivity is preserved only on ordered Ca/Pt4As8 layers, highlighting the importance of layer structure.

Contribution

It provides the first layer-by-layer characterization of this superconductor, linking structural order to the presence of superconductivity.

Findings

Superconducting coherence peaks observed only on ordered Ca/Pt4As8 layers.

Disordered Ca and Fe2As2 layers do not show superconducting features.

Ordered structure with charge balance is crucial for superconductivity.

Abstract

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.