Transport characteristics of epitaxial graphene proximitized to a two-dimensional Pb interface layer

Proximity coupling is an intriguing quantum concept to tune the properties of 2D materials, e.g., graphene. By intercalation of a Pb monolayer, a 2D heterostructure of charge-neutral graphene and a crystalline 2D Pb layer on SiC(0001) substrates was epitaxially grown. Thereby, microscopy revealed characteristic defects on microscopic and mesoscopic length scales, e.g., grain boundaries, substrate steps, and nonintercalated terraces. We analyzed in situ the electronic transport properties of this heterostructure. The systematic variation of the contact geometry and probe spacings, supplemented by finite-element simulations, allowed us to circumvent the problem of sample inhomogeneities and to determine reliably the conductivity of the 2D heterostructure itself. Thereby, the conductivity of (7±1)×10⁵0.16em0exS/m is comparable to values measured for monolayer and quasi-free monolayer graphene, but decreases with decreasing temperature down to 30 K, revealing a clear nonmetallic behavior. Our findings are compatible with a small gap opening (1--5 meV) in graphene due to the proximitized 2D Pb layer.