Local defects and ferromagnetism in graphene layers
TL;DR: In this article, the changes in the electronic structure induced by lattice defects in graphene planes were studied and it was shown that lattice distortions give rise to localized states at the Fermi level.
Abstract: We study the changes in the electronic structure induced by lattice defects in graphene planes. In many cases, lattice distortions give rise to localized states at the Fermi level. Electron-electron interactions lead to the existence of local moments. The RKKY interaction between these moments is always ferromagnetic, due to the semimetallic properties of graphene.
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TL;DR: In this paper, the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations, are discussed.
Abstract: This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.
20,824 citations
Cites background or methods from "Local defects and ferromagnetism in..."
...The existen e of these states anbe investigated by analyzing the s aling of the spe trumnear a defe t as a fun tion of the size of the system, L(Vozmediano et al., 2005)....
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...The existence of these states can be investigated by analyzing the scaling of the spectrum near a defect as a function of the size of the system, L (Vozmediano et al., 2005)....
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...At half- lling extended de-fe ts lead to an RKKY intera tion with an |r|−3 de-penden e (Dugaev et al., 2006; Vozmediano et al., 2005)....
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...At halffilling extended defects lead to an RKKY interaction with an |r|−3 dependence (Dugaev et al., 2006; Vozmediano et al., 2005)....
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TL;DR: In this paper, the electronic states of narrow graphene ribbons with zigzag and armchair edges were analyzed using the Dirac equation with appropriate boundary conditions, showing that the boundary condition allows a particlelike and a hole-like band with evanescent wave functions confined to the surfaces, which continuously turn into zero energy surface states as the width gets large.
Abstract: We study the electronic states of narrow graphene ribbons (``nanoribbons'') with zigzag and armchair edges. The finite width of these systems breaks the spectrum into an infinite set of bands, which we demonstrate can be quantitatively understood using the Dirac equation with appropriate boundary conditions. For the zigzag nanoribbon we demonstrate that the boundary condition allows a particlelike and a holelike band with evanescent wave functions confined to the surfaces, which continuously turn into the well-known zero energy surface states as the width gets large. For armchair edges, we show that the boundary condition leads to admixing of valley states, and the band structure is metallic when the width of the sample in lattice constant units has the form $3M+1$, with $M$ an integer, and insulating otherwise. A comparison of the wave functions and energies from tight-binding calculations and solutions of the Dirac equations yields quantitative agreement for all but the narrowest ribbons.
1,244 citations
TL;DR: In this article, the effects of localized (impurities or vacancies) and extended (edges or grain boundaries) defects on the electronic and transport properties of graphene are analyzed in a self-consistent way.
Abstract: Two-dimensional carbon, or graphene, is a semimetal that presents unusual low-energy electronic excitations described in terms of Dirac fermions. We analyze in a self-consistent way the effects of localized (impurities or vacancies) and extended (edges or grain boundaries) defects on the electronic and transport properties of graphene. On the one hand, point defects induce a finite elastic lifetime at low energies with the enhancement of the electronic density of states close to the Fermi level. Localized disorder leads to a universal, disorder independent, electrical conductivity at low temperatures, of the order of the quantum of conductance. The static conductivity increases with temperature and shows oscillations in the presence of a magnetic field. The graphene magnetic susceptibility is temperature dependent (unlike an ordinary metal) and also increases with the amount of defects. Optical transport properties are also calculated in detail. On the other hand, extended defects induce localized states near the Fermi level. In the absence of electron-hole symmetry, these states lead to a transfer of charge between the defects and the bulk, the phenomenon we call self-doping. The role of electron-electron interactions in controlling self-doping is also analyzed. We also discuss the integer and fractional quantum Hall effect in graphene, the role played by the edge states induced by a magnetic field, and their relation to the almost field independent surface states induced at boundaries. The possibility of magnetism in graphene, in the presence of short-range electron-electron interactions and disorder is also analyzed.
1,237 citations
TL;DR: In this article, an emerging Dirac liquid of Lorentz invariant quasi-particles in the weak coupling regime and strongly correlated electronic states in the strong coupling regime is discussed.
Abstract: 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.
988 citations
TL;DR: In this paper, a review of magnetic properties of spintronic devices based on carbon nanofragments and graphite is presented, with the help of computational examples based on simple model Hamiltonians.
Abstract: Magnetic materials and nanostructures based on carbon offer unique opportunities for future technological applications such as spintronics. This paper reviews graphene-derived systems in which magnetic correlations emerge as a result of reduced dimensions, disorder and other possible scenarios. In particular, zero-dimensional graphene nanofragments, one-dimensional graphene nanoribbons and defect-induced magnetism in graphene and graphite are covered. Possible physical mechanisms of the emergence of magnetism in these systems are illustrated with the help of computational examples based on simple model Hamiltonians. In addition, this review covers spin-transport properties, proposed designs of graphene-based spintronic devices, magnetic ordering at finite temperatures as well as the most recent experimental achievements.
981 citations
Cites background from "Local defects and ferromagnetism in..."
...The Ruderman-Kittel-KasuyaYoshida interaction is expected to be weak in this case due to the semi-metallic electronic structure of graphene (Brey and Fertig, 2006; Dugaev et al., 2006; Saremi, 2007; Vozmediano et al., 2005)....
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References
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TL;DR: Monocrystalline graphitic films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands and they exhibit a strong ambipolar electric field effect.
Abstract: We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10 13 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by applying gate voltage.
55,532 citations
TL;DR: In this paper, a perturbation calculation which starts with wave functions of the two-dimensional lattice and is applied to the three-dimensional graphite lattice is described and general features of the structure of the $\ensuremath{\pi}$ bands in the neighborhood of the zone edge are obtained and are expressed in terms of appropriate parameters.
Abstract: Tight-binding calculations, using a two-dimensional model of the graphite lattice, lead to a point of contact of valence and conduction bands at the corner of the reduced Brillouin zone. A perturbation calculation which starts with wave functions of the two-dimensional lattice and is applied to the three-dimensional lattice is described. Some general features of the structure of the $\ensuremath{\pi}$ bands in the neighborhood of the zone edge are obtained and are expressed in terms of appropriate parameters.
1,269 citations
TL;DR: Evidence that proton irradiation of energy 2.25 MeV on highly oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism is provided and magnetic ordering is stable at room temperature.
Abstract: We provide evidence that proton irradiation of energy 2.25 MeV on highly oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism. Measurements performed with a superconducting quantum interferometer device and magnetic force microscopy reveal that the magnetic ordering is stable at room temperature.
719 citations
TL;DR: In this paper, a system of electrons in the two-dimensional honeycomb lattice with Coulomb interactions is described by a renormalizable quantum field theory similar but not equal to QED3.
424 citations
TL;DR: In this paper, it was shown that hydrogenation of nanographite is able to induce finite magnetization and demonstrated the spontaneous magnetism of a graphene ribbon in which each carbon is bonded to two hydrogen atoms at one edge and to a single hydrogen atom at another edge.
Abstract: Hydrogenated nanographite can display spontaneous magnetism Recently we proposed that hydrogenation of nanographite is able to induce finite magnetization We have performed theoretical investigation of a graphene ribbon in which each carbon is bonded to two hydrogen atoms at one edge and to a single hydrogen atom at another edge Application of the local-spin-density approximation to the calculation of the electronic band-structure of the ribbon shows appearance of a spin-polarized flat band at the Fermi energy Producing different numbers of mono-hydrogenated carbons and di-hydrogenated carbons can create magnetic moments in nanographite
390 citations