Two-Dimensional Superconductivity of Ca-Intercalated Graphene on SiC: Vital Role of the Interface between Monolayer Graphene and the Substrate

Haruko Toyama; Ryota Akiyama; Satoru Ichinokura; Mizuki Hashizume; Takushi Iimori; Yukihiro Endo; Rei Hobara; Tomohiro Matsui; Kentaro Horii; Shunsuke Sato; Toru Hirahara; Fumio Komori; Shuji Hasegawa

doi:10.1021/acsnano.1c11161

Two-Dimensional Superconductivity of Ca-Intercalated Graphene on SiC: Vital Role of the Interface between Monolayer Graphene and the Substrate

ACS Nano. 2022 Mar 22;16(3):3582-3592. doi: 10.1021/acsnano.1c11161. Epub 2022 Feb 24.

Affiliations

¹ Department of Physics, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan.
² Department of Physics, Tokyo Institution of Technology, Meguro, Tokyo 152-8551, Japan.
³ The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.

PMID: 35209713
DOI: 10.1021/acsnano.1c11161

Abstract

Ca-intercalation has enabled superconductivity in graphene on SiC. However, the atomic and electronic structures that are critical for superconductivity are still under discussion. We find an essential role of the interface between monolayer graphene and the SiC substrate for superconductivity. In the Ca-intercalation process, at the interface a carbon layer terminating SiC changes to graphene by Ca-termination of SiC (monolayer graphene becomes a bilayer), inducing more electrons than a free-standing model. Then, Ca is intercalated in between the graphene layers, which shows superconductivity with the updated critical temperature (T_C) of up to 5.7 K. In addition, the relation between T_C and the normal-state conductivity is unusual, "dome-shaped". These findings are beyond the simple C₆CaC₆ model in which s-wave BCS superconductivity is theoretically predicted. This work proposes a general picture of the intercalation-induced superconductivity in graphene on SiC and indicates the potential for superconductivity induced by other intercalants.

Keywords: 2D materials; angle-resolved photoemission spectroscopy; electrical transport; graphene; intercalation; layered materials; superconductivity.