We present a new fabrication method for epitaxial graphene on SiC which enables the growth of ultrasmooth defect-and bilayer-free graphene sheets with an unprecedented reproducibility, a necessary prerequisite for wafer-scale fabrication of high quality graphene-based electronic devices. The inherent but unfavorable formation of high SiC surface terrace steps during high temperature sublimation growth is suppressed by rapid formation of the graphene buffer layer which stabilizes the SiC surface. The enhanced nucleation is enforced by decomposition of deposited polymer adsorbate which acts as a carbon source. Unique to this method are the conservation of mainly 0.25 and 0.5 nm high surface steps and the formation of bilayer-free graphene on an area only limited by the size of the sample. This makes the polymer-assisted sublimation growth technique a promising method for commercial wafer scale epitaxial graphene fabrication. The extraordinary electronic quality is evidenced by quantum resistance metrology at 4.2 K showing ultra-high precision and high electron mobility on mm scale devices comparable to state-of-the-art graphene.

Floquet engineering—the coherent dressing of matter via time-periodic perturbations—is a mechanism to realize and control emergent phases in materials out of equilibrium. However, its applicability to metallic quantum materials and semimetals such as graphene is an open question. The report of light-induced anomalous Hall effect in graphene remains debated, and a time-resolved photoemission experiment has suggested that Floquet effects might not be realizable in graphene and other semimetals with relatively short decoherence times. Here we provide direct spectroscopic evidence of Floquet effects in graphene through electronic structure measurements. We observe light–matter-dressed Dirac bands by measuring the contribution of Floquet sidebands, Volkov sidebands and their quantum path interference to graphene’s photoemission spectrum. Our results demonstrate that Floquet engineering in graphene is possible, even though ultrafast decoherence processes occur on the timescale of a few tens of femtoseconds. Our approach offers a way to experimentally realize Floquet engineering strategies in metallic and semimetallic systems and for the coherent stabilization of light-induced states with potentially non-trivial topological properties.

We report on electronic transport measurements in rotational square probe configuration in combination with scanning tunneling potentiometry (STP) of epitaxial graphene monolayers, which were fabricated by polymer-assisted sublimation growth on SiC substrates. The absence of bilayer graphene on the ultra-low step edges of below 0.75 nm scrutinized by AFM and STM result in a not yet observed resistance isotropy of graphene on 4H- and 6H-SiC(0001) substrates as low as 2%. We combine microscopic electronic properties with nano-scale transport experiments and thereby disentangle the underlying microscopic scattering mechanism to explain the remaining resistance anisotropy. Eventually, this can entirely be attributed to the resistance and the number of substrate steps which induce local scattering. Thereby, our data represent the ultimate limit for resistance isotropy of epitaxial graphene on SiC for the given miscut of the substrate.

Graphene, the first true two-dimensional material, still reveals the most remarkable transport properties among the growing class of two-dimensional materials. Although many studies have investigated fundamental scattering processes, the surprisingly large variation in the experimentally determined resistances is still an open issue. Here, we quantitatively investigate local transport properties of graphene prepared by polymer assisted sublimation growth using scanning tunneling potentiometry. These samples exhibit a spatially homogeneous current density, which allows to analyze variations in the local electrochemical potential with high precision. We utilize this possibility by examining the local sheet resistance finding a significant variation of up to 270% at low temperatures. We identify a correlation of the sheet resistance with the stacking sequence of the 6H silicon carbide substrate and with the distance between the graphene and the substrate. Our results experimentally quantify the impact of the graphene-substrate interaction on the local transport properties of graphene.

Generally, it is supposed that the Fermi level in epitaxial graphene is controlled by two effects: p‐type polarization doping induced by the bulk of the hexagonal silicon carbide (SiC)(0001) substrate and overcompensation by donor‐like states related to the buffer layer. The presented work is evidence that this effect is also related to the specific underlying SiC terrace. Here a periodic sequence of non‐identical SiC terraces is fabricated, which are unambiguously attributed to specific SiC surface terminations. A clear correlation between the SiC termination and the electronic graphene properties is experimentally observed and confirmed by various complementary surface‐sensitive methods. This correlation is attributed to a proximity effect of the SiC termination‐dependent polarization doping on the overlying graphene layer. These findings open a new approach for a nano‐scale doping‐engineering by the self‐patterning of epitaxial graphene and other 2D layers on dielectric polar substrates.