Structure of Superconducting Ca-intercalated Bilayer Graphene/SiC studied using Total-Reflection High-Energy Positron Diffraction

TL;DR

This study reveals the atomic structure of superconducting Ca-intercalated bilayer graphene on SiC using positron diffraction, showing Ca atoms intercalate between the buffer layer and graphene, and correlates this with a superconducting transition at 4K.

Contribution

First to identify the atomic arrangement of Ca in intercalated bilayer graphene and its relation to superconductivity using total-reflection high-energy positron diffraction.

Findings

Ca atoms intercalate in the graphene-buffer interlayer

Superconducting transition observed at 4K

Atomic structure correlates with superconductivity

Abstract

We have investigated the atomic structure of superconducting Ca-intercalated bilayer graphene on a SiC(0001) substrate using total-reflection high-energy positron diffraction. By comparing the experimental rocking-curves with ones calculated for various structural models using a full-dynamical theory, we have found that Ca atoms are intercalated in the graphene-buffer interlayer, rather than between the two graphene layers. From transport measurements, the superconducting transition was observed to be at Tc_onset = 4K for this structure. This study is the first to clearly identify the relation between the atomic arrangement and superconductivity in Ca-intercalated bilayer graphene.