We review the problem of electron-electron interactions in graphene. Starting from the screening of long range interactions in these systems, we discuss the existence of an emerging Dirac liquid of Lorentz invariant quasi-particles in the weak coupling regime, and strongly correlated electronic states in the strong coupling regime. We also analyze the analogy and connections between the many-body problem and the Coulomb impurity problem. The problem of the magnetic instability and Kondo effect of impurities and/or adatoms in graphene is also discussed in analogy with classical models of many-body effects in ordinary metals. We show that Lorentz invariance plays a fundamental role and leads to effects that span the whole spectrum, from the ultraviolet to the infrared. The effect of an emerging Lorentz invariance is also discussed in the context of finite size and edge effects as well as mesoscopic physics. We also briefly discuss the effects of strong magnetic fields in single layers and review some of the main aspects of the many-body problem in graphene bilayers. In addition to reviewing the fully understood aspects of the many-body problem in graphene, we show that a plethora of interesting issues remain open, both theoretically and experimentally, and that the field of graphene research is still exciting and vibrant.

Electron-Electron Interactions in Graphene: Current Status and Perspectives

Graphite as anode materials: Fundamental mechanism, recent progress and advances

The electronic structure of the crystalline fullerites C60 and C70 has been investigated by high-energy electron energy-loss spectroscopy in transmission. From valence band excitations and from core-level excitations of the C 1s level information on occupied and unoccupied π and ϖ bands has been obtained.

Electron energy-loss spectroscopy studies on C60 and C70 fullerite

The oxygen K edge of water and ice has been recorded with a resolution of 1 eV using x-ray Raman spectroscopy at 10 keV. The improved resolution allows for a clear observation of the strong pre-edge intensity in the liquid water spectrum. This is an independent experimental confirmation of this feature, which was recently detected by high-resolution soft-x-ray absorption spectroscopy and identified as a fingerprint of strongly asymmetric local configurations of the water molecules. The pre-edge peak as observed here with the truly bulk-sensitive x-ray Raman technique demonstrates that these configurations dominate the bulk of the liquid. Comparison with the K edge of ice gives an experimental limit on the fraction of fully coordinated waters in the liquid.

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X-ray Raman Spectroscopy at the Oxygen K Edge of Water and Ice: Implications on Local Structure Models

Inelastic scattering of X-rays and gamma rays by inner shell electrons

The dynamic structure factor S(q,\ensuremath{\omega}) of electrons in highly oriented pyrolytic graphite for q\ensuremath{\parallel}c and q\ensuremath{\perp}c with 0.37lql2.06 a.u. was measured at 0.8 eV resolution by inelastic scattering of synchrotron x radiation. The energy-transfer regions both of interband transitions and of core excitations were investigated. By means of Kramers-Kronig transformation Re[\ensuremath{\epsilon}(q,\ensuremath{\omega})] and Im[\ensuremath{\epsilon}(q,\ensuremath{\omega})] were obtained, where peaks of the latter were attributed directly to maxima of projections off the joint density of states achieved by both dipole selection rules and q-dependent matrix elements. Making use of both x-ray emission and photoemission data, limits for the energy positions of some conduction bands could be established by means of the Im[\ensuremath{\epsilon}(q,\ensuremath{\omega})] data. As far as weakly-${k}_{z}$-dispersing bands are concerned, their energy positions were found to be in good agreement with recent band-structure calculations. On the other hand, the measured energy ranges of the bands that could be identified as belonging to the recently proposed interlayer states disagree with most of the relevant band-structure calculations, though they are not far from the results of other spectroscopies. The strict bulk origin of the inelastic-scattering-based band-structure information obtained is stressed. The experimental data are also discussed in view of the interpretation of previous low-resolution inelastic-scattering data in terms of correlation-induced fine structure for q\ensuremath{\perp}c.

/pdf/interband-transitions-and-core-excitation-in-highly-oriented-4g4l5v8akt.pdf

Interband transitions and core excitation in highly oriented pyrolytic graphite studied by inelastic synchrotron x-ray scattering: Band-structure information.

A. Berthold

Papers

Interband transitions and core excitation in highly oriented pyrolytic graphite studied by inelastic synchrotron x-ray scattering: Band-structure information.

Information about the band structure of LiC6 from inelastic synchrotron X-ray scattering