We grow epitaxial graphene monolayers on Ru(0001) that cover uniformly the substrate over lateral distances larger than several microns. The weakly coupled graphene monolayer is periodically rippled and it shows charge inhomogeneities in the charge distribution. Real space measurements by scanning tunneling spectroscopy reveal the existence of electron pockets at the higher parts of the ripples, as predicted by a simple theoretical model. We also visualize the geometric and electronic structure of edges of graphene nanoislands.

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The electronic band structure of a material can acquire interesting topological properties in the presence of a magnetic field or as a result of the spin-orbit coupling [1][2][3] . We study graphene on Ir, with Pb monolayer islands intercalated between the graphene sheet and the Ir surface. Although the graphene layer is structurally una ected by the presence of the Pb islands, its electronic properties change markedly, with regularly spaced resonances appearing. We interpret these resonances as the e ect of a strong and spatially modulated spin-orbit coupling, induced in graphene by the Pb monolayer. As well as confined electronic states, the electronic spectrum has a series of gaps with non-trivial topological properties, resembling a realization of the quantum spin Hall e ect proposed by Bernevig and Zhang 4

We report on the magnetic properties of single Co atoms on graphene on Pt(111). By means of scanning tunneling microscopy spin-excitation spectroscopy, we infer a magnetic anisotropy of K ¼ À8:1 meV with out-of-plane hard axis and a magnetic moment of 2:2 B . Co adsorbs on the sixfold graphene hollow site. Upon hydrogen adsorption, three differently hydrogenated species are identified. Their magnetic properties are very different from those of clean Co. Ab initio calculations support our results and reveal that the large magnetic anisotropy stems from strong ligand field effects due to the interaction between Co and graphene orbitals. DOI: 10.1103/PhysRevLett.111.236801 PACS numbers: 73.22.Pr, 32.10.Dk, 75.30.Gw, 75.70.Rf Graphene is a promising material for spintronics due to the possibility of realizing controllable spin transport [1], its perfect spin filtering [2], and spin-relaxation lengths of several micrometers at room temperature [3]. Doping graphene by magnetic impurities opens further possibilities [4][5][6]. In particular, the creation of extended magnetic phases [7], quantum critical Kondo anomalies [8,9], and the strong scattering of spin currents [10] have been predicted. Moreover, for 3d metal atoms on graphene, the calculated uniaxial magnetic anisotropies [11,12] are beyond the current record value for a surface-adsorbed atom [13]. Furthermore, hydrogen adsorption has been predicted to change the spin of the adatoms [14], underlining its potential to tailor the magnetic properties. However, the predicted anisotropies and moments are highly controversial and largely depend on how electron correlations are treated. For the prototypical system of Co atoms on graphene, spin moments between 1 and 3 B and anisotropies of different signs have been calculated [12,[15][16][17]. At present, there is only one experiment addressing the magnetic properties of transition-metal adatoms on graphene. It reports on-top adsorption, a high-spin ground state, and weak magnetic anisotropy for Co=graphene=SiCð0001Þ [18].Here we present the first local measurement of the magnetic moment and anisotropy of individual Co atoms on graphene on Pt(111). This substrate was chosen since graphene binds very weakly to it [19], thus approaching freestanding graphene. Using scanning tunneling microscopy (STM) spin-excitation spectroscopy [20], we find an exceptionally large magnetic anisotropy of K ¼ À8:1 AE 0:4 meV with out-of-plane hard axis and a magnetic moment of 2:2 AE 0:4 B . Fully relativistic density functional theory (DFT) calculations show the anisotropy to be mainly a hybridization effect. In addition to clean Co, we identify three hydrogenated species, CoH n , n 2 f1; 2; 3g, with very different magnetic behavior. The coexistence of clean and hydrogenated adatoms is expected to be a general feature of transition metal atoms on graphene that has to be considered in the interpretation of any ensemble measurement.The experiments were performed with a homebuilt STM operating at T ¼ 0:4 K and in magnetic fields up to ...