STM observation of the surface state of graphene on SiC with deposition of group 14 metals Pb and Sn

抄録

Proximity-induced superconductivity in graphene has been recently studied with great interest because the introduction of superconductivity to the Dirac fermions is very attractive in terms of both fundamental physics and technological applications. In this case, the group 14 elements Pb (T_c = 7.2 K) and Sn (T_c = 3.7 K) is preferred as candidate materials to induce superconductivity. Previously we have studied the superconducting properties for Pb-deposited bilayer graphene on SiC(0001) substrate by ultralow-temperature scanning tunneling microscope (STM) measurement, and we observed that Pb atoms form islands in the VW growth mode. We also observed a superconducting gap on graphene, which was induced by the proximity effect from the Pb islands. This is similar to a previous study by another group [1], using a quasi-free-standing monolayer graphene obtained by large scale hydrogen intercalation underneath graphene on 6H-SiC.

Here we focus on Sn-deposited graphene. Kessler et al. reported that Sn atoms form amorphous-like islands on exfoliated graphene [2]. They also demonstrated superconducting behavior of electrical conductivity. On the other hand, Kim et al. reported Sn atoms intercalate into the graphene/SiC(0001) and form an atomic-layer between graphene and SiC substrate [3]. To elucidate the origin of superconducting properties in Sn-deposited graphene on SiC, it is necessary to clarify the morphology of the surface during the Sn-deposition process.

In this study, we demonstrate the surface morphology of bilayer graphene/SiC(0001) in samples with different amounts of Sn deposition, observed by using STM. Figure 1(a) shows the STM image of about 10 ML Sn-deposited bilayer graphene. The Sn atoms were deposited on bilayer graphene at room temperature. One can see that crevasse-like groove structures are formed on graphene while no island-like structures were observed. These grooves are created across the terrace steps of the SiC substrate. As seen in Figure 1(b), its depth is estimated to be roughly 0.7 nm, which corresponds to an interlayer distance of graphene layers. These results suggest that Sn atoms penetrate the graphene by partially disrupting the graphene during the initial process of Sn deposition. In my presentation, we will present the results of STM experiments measured on samples with different amounts of Sn deposition and discuss the possibility of Proximity-induced superconductivity in bilayer graphene on SiC.

[1] F. Paschke, et al., Adv. Quantum Technol, 3, 2000082 (2020).

[2] B. M. Kessler, et al., Phys. Rev. Lett. 104, 047001 (2010).

[3] H. Kim, et al., J. Phys. D: Appl. Phys. 49. 135307 (2016).