Realistic large-scale modeling of Rashba and induced spin-orbit effects in graphene/high-Z-metal systems

Graphene, as a material with a small intrinsic spin-orbit interaction of approximately 1 $\mu$eV, has a limited application in spintronics. Adsorption of graphene on the surfaces of heavy-metals was proposed to induce the strong spin-splitting of the graphene $\pi$-bands either via Rashba effect or due to the induced spin-orbit effects via hybridization of the valence band states of graphene and metal. The spin-resolved photoelectron spectroscopy experiments performed on graphene adsorbed on the substrates containing heavy elements demonstrate the "giant" spin-splitting of the $\pi$ states of the order of 100 meV in the vicinity of the Fermi level ($E_F$) and the K point. However, the recent scanning tunneling spectroscopy experiments did not confirm these findings, leaving the fact of the observation of the "giant" Rashba effect or induced spin-orbit interaction in graphene still open. Thus, a detailed understanding of the physics in such systems is indispensable. From a theory side this requires, first of all, correct modeling of the graphene/metal interfaces under study. Here we present realistic super-cell density-functional theory calculations, including dispersion interaction and spin-orbit interaction, for several graphene/high-Z-metal interfaces. While correctly reproduce the spin-splitting features of the metallic surfaces, their modifications under graphene adsorption and doping level of graphene, our studies reveal that neither "giant" Rashba- nor spin-orbit induced splitting of the graphene pi states around $E_F$ take place.Comment: accepted for publicatio

Playing graphene nanodrums: force spectroscopy of graphene on Ru(0001)

Graphene, a thinnest material in the world, can form moire structures on different substrates, including graphite, h-BN, or metal surfaces. In such systems the structure of graphene, i. e. its corrugation, as well as its electronic and elastic properties are defined by the combination of the system geometry and local interaction strength at the interface. The corrugation in such structures on metals is heavily extracted from diffraction or local probe microscopy experiments and can be obtained only via comparison with theoretical data, which usually simulate the experimental findings. Here we show that graphene corrugation on metals can be measured directly employing atomic force spectroscopy and obtained value coincides with state-of-the-art theoretical results. We also address the elastic reaction of the formed graphene nanodoms on the indentation process by the scanning tip that is important for the modeling and fabrication of graphene-based nanoresonators on the nanoscale.Comment: manuscript and supplementary materia

First multi-reference correlation treatment of bulk metals

Existence of the sp-d hybridization of the valence band states of the fcc Ca and Sr in the vicinity of the Fermi level indicates that their electronic wave function can have a multi-reference (MR) character. We performed a wave function-based correlation treatment for these materials by means of the method of increments. As oppose to the single-reference correlation treatment (here: coupled cluster), which fails to describe cohesive properties in both cases, employing the MR averaged coupled pair functional one can achieve almost 100 % of the experimental correlation energy.Comment: 16 pages, 8 figures, 3 table

Graphene growth and properties on metal substrates

Graphene-metal interface as one of the interesting graphene-based objects attracts much attention from both application and fundamental science points of view. This paper gives a timely review of the recent experimental works on the growth and the electronic properties of the graphene-metal interfaces. This work makes a link between huge amount of experimental and theoretical data allowing one to understand the influence of the metallic substrate on the electronic properties of a graphene overlayer and how its properties can be modified in a controllable way. The further directions of studies and applications of the graphene-metal interfaces are discussed.Comment: 30 pages, 18 figure

Comment on "Spin-Orbit Coupling Induced Gap in Graphene on Pt(111) with Intercalated Pb Monolayer"

Recently a paper of Klimovskikh et al. was published presenting experimental and theoretical analysis of the graphene/Pb/Pt(111) system. The authors investigate the crystallographic and electronic structure of this graphene-based system by means of LEED, ARPES, and spin-resolved PES of the graphene $\pi$ states in the vicinity of the Dirac point of graphene. The authors of this paper demonstrate that an energy gap of approx. 200 meV is opened in the spectral function of graphene directly at the Dirac point of graphene and spin-splitting of 100 meV is detected for the upper part of the Dirac cone. On the basis of the spin-resolved photoelectron spectroscopy measurements of the region around the gap the authors claim that these splittings are of a spin-orbit nature and that the observed spin structure confirms the observation of the quantum spin Hall state in graphene, proposed in earlier theoretical works. Here we will show that careful systematic analysis of the experimental data presented in this manuscript is needed and their interpretation require more critical consideration for making such conclusions. Our analysis demonstrates that the proposed effects and interpretations are questionable and require further more careful experiments.Comment: submitted: 02.02.2017; accepted: 09.03.201

Multichannel scanning probe microscopy and spectroscopy of graphene moire structures

The graphene moire structures on metals, as they demonstrate both long (moire) and short (atomic) scale ordered structures, are the ideal systems for the application of scanning probe methods. Here we present the complex studies of the graphene/Ir(111) system by means of 3D scanning tunnelling and atomic force microscopy/spectroscopy as well as Kelvin-probe force microscopy. All results clearly demonstrate a variation of the moire and atomic scale contrasts as a function of the bias voltage as well as the distance between the scanning probe and the sample, allowing to discriminate between topographic and electronic contributions in the imaging of a graphene layer on metals. The presented results are accompanied by the state-of-the-art density functional theory calculations demonstrating the excellent agreement between theoretical and experimental data.Comment: 30 pages, 13 figures, submitted on 20.09.201

Restoring a free-standing character of graphene on Ru(0001)

Realization of a free-standing graphene is always a demanding task. Here we use scanning probe microscopy and spectroscopy to study the crystallographic structure and electronic properties of the uniform free-standing graphene layers obtained by intercalation of oxygen monolayer in the "strongly" bonded graphene/Ru(0001) interface. Spectroscopic data show that such graphene layer is heavily p-doped with the Dirac point located at 552 meV above the Fermi level. Experimental data are understood within DFT and the observed effects are in good agreement with the theoretical data.Comment: manuscript and supplementary materia

Scanning probe microscopy and spectroscopy of graphene on metals

Graphene, a two-dimensional (2D) material with unique electronic properties, appears to be an ideal object for the application of surface-science methods. Among them, a family of scanning probe microscopy methods (STM, AFM, KPFM) and the corresponding spectroscopy add-ons provide information about the structure and electronic properties of graphene on the local scale (from inline imagem to atoms). This review focuses on the recent applications of these microscopic/spectroscopic methods for the investigation of graphene on metals (interfaces, intercalation-like systems, graphene nanoribbons, and quantum dots, etc.). It is shown that very important information about interaction strength at the graphene/metal interfaces as well as about modification of the electronic spectrum of graphene at the Fermi level can be obtained on the local scale. The combination of these results with those obtained by other methods and comparison with recent theoretical data demonstrate the power of this approach for the investigation of the graphene-based systems.Comment: Feature Article in pss (b

General approach to the understanding the electronic structure of graphene on metals

This manuscript presents the general approach to the understanding of the connection between bonding mechanism and electronic structure of graphene on metals. To demonstrate its validity, two limiting cases of the "weakly" and "strongly" bonded graphene on Al(111) and Ni(111) are considered, where the Dirac cone is preserved or fully destroyed, respectively. Furthermore, the electronic structure, i. e. doping level, hybridization effects, as well as a gap formation at the Dirac point of the intermediate system, graphene/Cu(111), is fully understood in the framework of the proposed approach. This work summarises the long-term debates regarding connection of the bonding strength and the valence band modification in the graphene/metal systems and paves a way for the effective control of the electronic states of graphene in the vicinity of the Fermi level.Comment: manuscript and supplementary materia

Adsorption of NO2 on WSe2: DFT and photoelectron spectroscopy studies

The electronic structure modifications of WSe2 upon NO2-adsorption at room and low temperatures were studied by means of photoelectron spectroscopy. We found only moderate changes in the electronic structure, which are manifested as an upward shift of the WSe2-related bands to the smaller binding energies. The observed effects are modelled within the density functional theory approach, where a weak adsorption energy of gas molecules on the surface of WSe2 was deduced. The obtained experimental data are explained as a valence bands polarisation effect, which causes their energy shift depending on the adsorption geometry and the formed dipole moment.Comment: manuscript and supplementary materia