Intact Dirac Cones at Broken Sublattice Symmetry: Photoemission Study of Graphene on Ni and Co

Varykhalov, A.; Marchenko, D.; Sánchez-Barriga, J.; Scholz, Markus; Verberck, Bart; Trauzettel, Björn; Wehling, T. O.; Carbone, C.; Rader, O.

doi:10.1103/physrevx.2.041017

Cited by 83 publications

(154 citation statements)

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“…Where, instead, an unexpected Dirac point forms at higher binding energy as part of a pair of bonding and antibonding Dirac cones [12]. These cones have been found to be highly spin polarized by the exchange interaction from the substrate [13,14].…”

Section: Introductionmentioning

confidence: 99%

Rashba splitting of 100 meV in Au-intercalated graphene on SiC

Marchenko

Varykhalov

Sánchez-Barriga

et al. 2016

Applied Physics Letters

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Intercalation of Au can produce giant Rashba-type spin-orbit splittings in graphene but this has not yet been achieved on a semiconductor substrate. For graphene/SiC(0001), Au intercalation yields two phases with different doping. Here, we report the preparation of an almost pure p-type graphene phase after Au intercalation. We observe a 100 meV Rashba-type spin-orbit splitting at 0.9 eV binding energy. We show that this giant splitting is due to hybridization and much more limited in energy and momentum space than for Au-intercalated graphene on Ni. In a future spintronics, graphene could be used in various ways: as efficient leads for spin currents due to low spin-orbit interaction and large spin relaxation lengths [1], as ferromagnetic graphene due to a proximity magnetization [2], as spin filter when a large Rashba type spin-orbit interaction and a band gap at the Dirac point are imposed by a substrate [3], or when the spin-orbit interaction is strongly enhanced by covalently bonded adatoms [4]. The Rashba effect on a graphene Dirac cone leads to a complex band topology with a gapped and an ungapped cone similar to spinless bilayer graphene [5,6]. It has been shown by ARPES that for Au-intercalated graphene/Ni(111) the Dirac cone is intact [7] and gapless [8]. A giant Rashba splitting of ∼ 100 meV was found for graphene/Au/Ni(111) [9].On light elements, the spin-orbit splitting of graphene cannot be resolved in experiment, this is the case with Ni(111) and Co(0001) [10,11]. Where, instead, an unexpected Dirac point forms at higher binding energy as part of a pair of bonding and antibonding Dirac cones [12]. These cones have been found to be highly spin polarized by the exchange interaction from the substrate [13,14].The interfaces of graphene with metals are structurally rather well defined, and the intercalation of Au is driven by the transition metal substrate. The creation of the spinorbit interaction in the graphene is well understood based on spin-dependent hybridization with d-states of the substrate. This is the case for graphene/Au/Ni(111) [9] and is confirmed indirectly by the vanishing spin-orbit splitting of the graphene-Bi interface because atomic numbers of Bi and Au are similar but hybridization with d-states is possible only for Au [15]. A similar hybridization causes the ∼ 50 meV spin-orbit splitting for graphene/Ir (111) [16].To make the aforementioned effects useful for spintronics, they have to be confirmed on an insulating substrate such as SiC because otherwise the metallic substrate will dominate charge and spin transport. On bare SiC, graphene does not show an enhanced spin-orbit splitting as has been clarified by spin-resolved photoemission [17]. Recently, a spin-orbit splitting of 17 meV has been measured for graphene on the semiconductor WS 2 [18].In the context of a possible p-doping of graphene by metals, the intercalation of Au under graphene on SiC has already been studied [19,20], which serves as starting point for our search for enhanced spin-orbit splittings in this s...

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Section: Introductionmentioning

confidence: 99%

Rashba splitting of 100 meV in Au-intercalated graphene on SiC

Marchenko

Varykhalov

Sánchez-Barriga

et al. 2016

Applied Physics Letters

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“…In contrast, in the weakly physisorbed hcpfcc graphene conformation, the π-band does not strongly interact with the Ni(111) bands due to the larger adsorption distance, and, consequently, the linear dispersion prevails. In that case, the 3 influence of the substrate results only in a small shift of the Dirac point with respect to the Fermi level, i.e., a small doping effect [16].…”

Section: Introductionmentioning

confidence: 99%

“…Initially ab initio Density Functional Theory (DFT) studies relied on the Local Density Approximation (LDA), which could apparently correctly discern between physisorbed and chemisorbed states [16]. Nowadays this is known to happen because of the LDA exchangecorrelation functionals tend to overbind [19].…”

Section: Introductionmentioning

confidence: 99%

The contact of graphene with Ni(111) surface: description by modern dispersive forces approaches

et al. 2016

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Here we present a Density Functional Theory (DFT) study on the suitability of modern corrections for the inclusion of dispersion related terms (DFT-D) in treating the interaction of graphene and metal surfaces, exemplified by the graphene/Ni(111) system. The Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional is used as basis, on top of which we tested the family of Grimme corrections (D2 and D3, including Becke-Jonson damping and Andersson approach) as well as different flavors of the approach by Tkatchenko and Scheffler (TS). Two experimentally observed chemisorbed states, top-fcc and bridge-top conformations, were examined, as well as one physisorbed situation, the hcp-fcc state. Geometric, energetic, and electronic properties were compared to sets of experimental data for our model system of graphene/Ni(111), but also for available data of bulk Ni, graphite, and free-standing graphene. Results show that two of the most recent approximations, the fully ab initio TS-MBD, and the semi-empirical Grimme D3 correction are best suited to describe graphene↔metal contacts, yet, comparing to earlier studies, the Rev-vdW-DF2 functional is also a good option, whereas optB86-vdW and optB88b-vdW functionals are fairly close to experimental values to be harmless used. The present results highlight how different approaches for the approximate treatment of dispersive forces yield different results, and so finetuning and testing of the envisioned approach for every specific system is advisable. The present survey clears the path for future accurate and affordable theoretical studies of nanotechnologic devices based on graphene-metal contacts.

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“…It should be noticed that there is another surface, which is very similar to Ni(111) regarding its crystal structure and properties, namely Co(0001). Graphene can be easily grown on this substrate, 28 and a (1 Â 1) structure can be obtained at certain conditions; 29,30 however, no studies of doped graphene on this type of surface have been reported yet.…”

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confidence: 99%

Epitaxial B-Graphene: Large-Scale Growth and Atomic Structure

et al. 2015

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Embedding foreign atoms or molecules in graphene has become the key approach in its functionalization and is intensively used for tuning its structural and electronic properties.Here, we present an efficient method based on chemical vapor deposition for large scale growth of boron-doped graphene (B-graphene) on Ni(111) and Co(0001) substrates using carborane molecules as the precursor. It is shown that up to 19 at. % of boron can be embedded in the graphene matrix and that a planar CÀB sp 2 network is formed. It is resistant to air exposure and widely retains the electronic structure of graphene on metals. The large-scale and local structure of this material has been explored depending on boron content and substrate. By resolving individual impurities with scanning tunneling microscopy we have demonstrated the possibility for preferential substitution of carbon with boron in one of the graphene sublattices (unbalanced sublattice doping) at low doping level on the Ni(111) substrate. At high boron content the honeycomb lattice of B-graphene is strongly distorted, and therefore, it demonstrates no unballanced sublattice doping.

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Intact Dirac Cones at Broken Sublattice Symmetry: Photoemission Study of Graphene on Ni and Co

Cited by 83 publications

References 44 publications

Rashba splitting of 100 meV in Au-intercalated graphene on SiC

Rashba splitting of 100 meV in Au-intercalated graphene on SiC

The contact of graphene with Ni(111) surface: description by modern dispersive forces approaches

Epitaxial B-Graphene: Large-Scale Growth and Atomic Structure

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