Effect of electron-electron interaction on the Fermi surface topology of doped graphene

Roldán, Rafael; Sancho, M. P. López; Guinea, F.

doi:10.1103/physrevb.77.115410

Cited by 56 publications

(41 citation statements)

References 53 publications

(78 reference statements)

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“…Such effects were predicted generally for 2D systems [5] and for graphene [6]. This is also supported by the more favorable agreement of the GW model, which partially accounts for the e-e interaction.…”

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confidence: 67%

“…By this method, we can induce an electronic topological transition in graphene for the first time, whereby the Fermi energy E F is brought to the position of the saddle point VHS in graphene. We find that the electronic structure is strongly renormalized by the resulting DOS divergence such that the VHS has an extended, not pointlike, character [5,6]; feeding the experimental Fermi surface topology into a calculation of the screened Coulomb interaction, we predict the system is unstable to superconducting pairing due to electron-electron interactions.Clean graphene on SiC(0001) was prepared as before [7,8], and various combinations of K and Ca were used as dopants. Ca could be intercalated under the graphene by repeated cycles of Ca deposition and annealing onto slightly incomplete graphene layers, which consist of isolated, but nearly merged islands of monolayer graphene.…”

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Extended van Hove Singularity and Superconducting Instability in Doped Graphene

et al. 2010

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We have investigated the effects of doping on a single layer of graphene using angle-resolved photoemission spectroscopy. We show that many-body interactions severely warp the Fermi surface, leading to an extended van Hove singularity (EVHS) at the graphene M point. The ground state properties of graphene with such an EVHS are calculated, analyzing the competition between a magnetic instability and the tendency towards superconductivity. We find that the latter plays the dominant role as it is enhanced by the strong modulation of the interaction along the Fermi line, leading to an energy scale for the onset of the pairing instability as large as 1 meV when the Fermi energy is sufficiently close to the EVHS. DOI: 10.1103/PhysRevLett.104.136803 PACS numbers: 73.22.Pr, 73.20.At, 74.70.Wz, 79.60.Ài The fundamental interactions between charge, spin, and lattice depend very much on the topology of electronic bands, particularly in two dimensions when the Fermi level E F is near a saddle point. Such a saddle point occurs where the curvature of the bands has opposite sign in two orthogonal directions, leading to a van Hove singularity (VHS), i.e., a divergence in the density of states (DOS).Much attention has been given to a ''VHS scenario'' in the cuprates, whereby the superconductivity is strongly influenced or even induced by a saddle point VHS [1,2]. Among the important effects of the VHS are (1) the presence of both electronlike and holelike carriers, leading to an attractive potential favoring pairing, (2) a high DOS, held to favor not only superconductivity but structural and magnetic instabilities, and (3) a perfect screening at wave vectors connecting VHSs, which acts to reduce repulsion. The topology of the VHS is important, especially when the curvature of one band vanishes; i.e., the electron or hole mass diverges. This increases the strength of the divergence in the DOS at such a so-called extended VHS (EVHS), which can increase the critical temperature for superconductivity [3].Graphene's band structure has saddle points at the M point of the Brillouin zone (BZ) occurring around AE2 eV from the charge neutrality point at the Dirac energy E D [4]. Since superconductivity occurs in graphene-related systems such as graphite-intercalation compounds and nanotubes, it is interesting to explore whether superconductivity or other instability can appear in graphene itself due to the influence of this VHS.In this Letter, we present the band structure of highly doped graphene determined by angle-resolved photoemission spectroscopy (ARPES). We show that by chemically doping graphene on both sides, a much higher level of doping can be achieved than previously obtained. By this method, we can induce an electronic topological transition in graphene for the first time, whereby the Fermi energy E F is brought to the position of the saddle point VHS in graphene. We find that the electronic structure is strongly renormalized by the resulting DOS divergence such that the VHS has an extended, not pointlike, character [5,6]...

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Extended van Hove Singularity and Superconducting Instability in Doped Graphene

et al. 2010

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“…[11][12][13] This term leads to a deformation of the band dispersion toward the saddle point, 12 an effect that has been observed experimentally by angle-resolved photoemission spectroscopy. 6 Notice that longer-range interaction terms, such as the nearest-neighbor repulsion, would lead to a richer phase diagram, with the possibility of a Pomeranchuk instability.…”

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confidence: 92%

Spin-density-wave instability in graphene doped near the van Hove singularity

et al. 2011

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We study the instability of the metallic state toward the formation of a different ground state in graphene doped near the van Hove singularity. The system is described by the Hubbard model and a field theoretical approach is used to calculate the charge and spin susceptibility. We find that for repulsive interactions, within the random phase approximation, there is a competition between ferromagnetism and the spin-density wave (SDW). It turns out that a SDW with a triangular geometry is more favorable when the Hubbard parameter is above the critical value U c (T ), which depends on the temperature T , even if there are small variations in the doping. Our results can be verified by angle-resolved photoemission spectroscopy or neutron scattering experiments in highly doped graphene.

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“…We attribute these variations to velocity renormalization effects due to electron-electron interactions 38 .…”

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Microscopic polarization in bilayer graphene

et al. 2011

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Bilayer graphene has drawn significant attention due to the opening of a band gap in its low energy electronic spectrum, which offers a promising route to electronic applications. The gap can be either tunable through an external electric field or spontaneously formed through an interaction-induced symmetry breaking. Our scanning tunneling measurements reveal the microscopic nature of the bilayer gap to be very different from what is observed in previous macroscopic measurements or expected from current theoretical models. The potential difference between the layers, which is proportional to charge imbalance and determines the gap value, shows strong dependence on the disorder potential, varying spatially in both magnitude and sign on a microscopic level. Furthermore, the gap does not vanish at small charge densities. Additional interaction-induced effects are observed in a magnetic field with the opening of a subgap when the zero orbital Landau level is placed at the Fermi energy.Bilayer graphene consists of two graphene sheets overlaid in the Bernal stacking orientation where A 2 atoms of the top layer lie on top of the B 1 atoms of the bottom layer (see * These authors contributed equally to this work.§ To whom correspondence should be addressed: nikolai.zhitenev@nist.gov, joseph.stroscio@nist.gov.2 Fig. 1a), connected by the interlayer coupling 1 γ , thus breaking the A/B sublattice symmetry in the individual graphene layers. This results in massive chiral fermions where the electronic energy dispersion is hyperbolic in momentum, in contrast to the linear dispersion that leads to massless carriers in single layer graphene 1,2 . In bilayer graphene the energy bands still meet at the charge neutrality point (E D ) in the absence of an electric field between the layers (neglecting interaction effects) (Fig. 1b). In an applied electric field a potential asymmetry is developed between the layers, resulting in the opening of an energy band gap between the low lying bands making bilayer graphene of intense interest in electronic applications ( Fig. 1b) [2][3][4][5][6][7][8][9][10] . Bilayer graphene also differs from single layer graphene in its magnetic quantization in the quantum Hall regime. At E D , the four-fold degenerate Landau level (LL) in single layer graphene becomes eight-fold degenerate in the bilayer due to the additional layer degeneracy 3,11,12 . When the gap is opened this manifold splits into two four-fold degenerate quartets polarized on each layer at low energies. Lifting of these degeneracies have been observed in recent measurements [13][14][15][16] .Theoretical studies 17,18 suggest the existence of interaction-driven band gaps, which are even possible in zero applied field with corresponding quantum Hall ferromagnetic states 17,19 .The energy band gap in bilayer graphene has been studied by optical measurements such as angle resolved photoemission spectroscopy 20 and infrared spectroscopy [4][5][6]21 , which demonstrate that the gap is externally tunable and can reach values up to ≈ 250 meV...

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Effect of electron-electron interaction on the Fermi surface topology of doped graphene

Cited by 56 publications

References 53 publications

Extended van Hove Singularity and Superconducting Instability in Doped Graphene

Extended van Hove Singularity and Superconducting Instability in Doped Graphene

Spin-density-wave instability in graphene doped near the van Hove singularity

Microscopic polarization in bilayer graphene

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