Superconductivity in monolayer graphene driven by Ca and K doping

Superconductivity (SC) induced in graphene has been attracting much attention recently [1, 2]. An example is Ca-intercalated bilayer graphene on SiC [1]. Our structural analysis has unveiled that Ca is intercalated in graphene-buffer interlayer [3], not in graphene-graphene interlayer as analogy of graphite intercalation. Because the position of Ca atoms is on the buffer layer, it can be expected to intercalate Ca atoms into monolayer graphene on SiC. In this study, we have fabricated three samples: Ca-intercalated monolayer graphene grown on SiC(0001), and K or Ca+K adsorbed one on it to change the carrier concentration. Transport measurements have been performed in situ in ultrahigh vacuum. The result shows SC transition at (T_c =) 5.5 K, 3.2 K and 1.6 K, respectively. This is the first report of SC in monolayer graphene which has Dirac electrons. The relation between the T_c and the carrier density is different from that of the conventional SC. In the presentation, we will show the details of the experiments and discuss the mechanism of SC. This work was supported by JSPS KAKENHI Grant Number 18K18732, 18K19014, and JSPS fellows.