Direct Observation of Superconductivity in Calcium-Intercalated Bilayer Graphene by in situ Electrical Transport Measurements

TL;DR

This study demonstrates superconductivity in calcium-intercalated bilayer graphene with a transition temperature of 4.0 K, confirmed through in situ electrical transport measurements, highlighting the role of a free-electron-like metallic band.

Contribution

First direct observation of superconductivity in Ca-intercalated bilayer graphene using in situ measurements, confirming theoretical predictions about the role of electronic structure.

Findings

C$_6$CaC$_6$ exhibits superconductivity at 4.0 K.

C$_6$LiC$_6$ does not show superconductivity.

Superconductivity correlates with a free-electron-like metallic band at the Fermi level.

Abstract

We report the superconductivity in Ca-intercalated bilayer graphene C$_6$CaC$_6$, the thinnest limit of Ca graphite intercalation compound. We performed \textit{in situ} electrical transport measurements on pristine bilayer graphene, C$_6$LiC$_6$ and C$_6$CaC$_6$ fabricated on SiC substrate under zero and non-zero magnetic field. While both bilayer graphene and C$_6$LiC$_6$ show non-superconducting behavior, C$_6$CaC$_6$ exhibits the superconductivity with transition temperature ($T_{{\rm c}}$) of 4.0 K. The observed $T_{{\rm c}}$ in C$_6$CaC$_6$ and the absence of superconductivity in C$_6$LiC$_6$ show a good agreement with the theoretical prediction, suggesting the importance of a free-electron-like metallic band at the Fermi level to drive the superconductivity.