Hydrogen‐Intercalated Graphene on SiC as Platform for Hybrid Superconductor Devices

Abstract

Nanodevices based on hybrid graphene-superconductor structures have recently attracted much attention owing to both fundamental and application aspects. However, atomic-level investigations of proximity-induced superconductivity in graphene, especially on technologically relevant substrates remain rare. Here, the atomic-scale study of electronic properties and the superconducting proximity effect in hydrogen-intercalated single-layer graphene on SiC decorated with epitaxial lead (Pb) islands is reported. The graphene layer is thoroughly characterized by means of Landau level spectroscopy which confirms its quasi-free-standing nature. Scanning tunneling spectroscopy performed at 1.8 K on the graphene layer in the vicinity of Pb islands shows a reduced superconducting gap of gr = 0.20(1) meV, which points to a graphene/superconductor junction of moderate transparency. The variations of the proximity-induced superconducting gap on graphene are measured as function of spatial position as well as of magnetic field strength. Spatially resolved measurements yield a coherence length of about 175 nm in the graphene monolayer. The study provides a foundation for realization of graphene-superconductor heterostructures on large-scale SiC(0001) wafers suitable for future technological applications.

Shaping Graphene Superconductivity with Nanometer Precision

“…In contrast, the values of Δ G , obtained from dI/dV spectra close to the islands, varies strongly for different Pb‐graphene junctions, ranging from Δ G = 1.2 meV, very close to bulk Pb ( Δ Pb = 1.35 meV), to Δ G = 0.6 meV. These Δ G values are all significantly larger than the proximity‐induced gaps by Pb islands on hydrogen‐intercalated single‐layer graphene on SiC(0001), where values around Δ G = 0.2 meV have been reported, [18] indicating that in the present case the Pb‐graphene interface has a larger transparency. The typical values employed in our fits for the broadening or Dynes’ parameter Γ G are on the order of 0.1 Δ Pb , which are quite standard for strong‐coupling superconductors like Pb [17] .…”

“…In all these systems room‐temperature evaporation of Pb resulted in the formation of triangular Pb islands, similar to those shown on graphene on SiC(000‐1) (refer to Figures S1 and S2, Supporting Information and refs. [18,30,35). Our results on these surfaces reveal that in all cases bulk‐like superconductivity persists in Pb islands, inducing superconducting properties to the surrounding graphene regions.…”

“…[10][11][12] However, after this promising initial stage, mostly focused on the transport properties of graphene-superconductor hybrids, the experimental progress in the field has been relatively scarce. [13][14][15] This has likely been due to the difficulties in controlling the preparation of clean samples with well-defined graphene superconductor junctions [14,15] and the lack of local probe experiments providing more direct information about the superconductivity in graphene [16][17][18] It was only very recently that graphene superconductivity made a disruptive advance with the appearance of twisted bilayers. [19][20][21][22][23][24] Here, we present a new method, based on the proximity effect in combination with scanning tunnelling microscopy (STM) manipulation capabilities, [25,26] that offers an unprecedented control of graphene superconductivity.…”

Observation of Yu–Shiba–Rusinov States in Superconducting Graphene

“…On this graphene surface, we deposit 5-15 monolayers (ML) of Pb at a rate of 3-10 ML min −1 while maintaining the sample at room temperature. [34,35] As a result, several triangular Pb islands with heights between 2 and 10 nm and sides between 20 and 300 nm are formed, see Figure 1a.…”

Momentum microscopy of Pb-intercalated graphene on SiC: charge neutrality and electronic structure of interfacial Pb

“…In fact, proximity spin-orbit coupling has been induced in Pb-intercalated graphene, yet only on metallic Ir and Pt substrates [30][31][32]. On the other hand, proximity superconductivity has been reported in quasi-freestanding monolayer graphene on SiC decorated with Pb islands [33,34]. Regarding the very limited extent of this lateral proximity effect into graphene, the homogeneous intercalation of Pb underneath could be a pragmatic workaround as it might even give rise to vertical proximity coupling that spreads over the entire layer.…”