Born-Oppenheimer breakdown in graphene
Simone Pisana,Michele Lazzeri,Cinzia Casiraghi,K. S. Novoselov,A. K. Geim,Andrea C. Ferrari,Francesco Mauri +6 more
TLDR
The Born-Oppenheimer approximation (BO) has proven effective for the accurate determination of chemical reactions, molecular dynamics and phonon frequencies in a wide range of metallic systems as discussed by the authors.Abstract:
The Born-Oppenheimer approximation (BO) has proven effective for the accurate determination of chemical reactions, molecular dynamics and phonon frequencies in a wide range of metallic systems. Graphene, recently discovered in the free state, is a zero band-gap semiconductor, which becomes a metal if the Fermi energy is tuned applying a gate-voltage Vg. Graphene electrons near the Fermi energy have twodimensional massless dispersions, described by Dirac cones. Here we show that a change in Vg induces a stiffening of the Raman G peak (i.e. the zone-center E2g optical phonon), which cannot be described within BO. Indeed, the E2g vibrations cause rigid oscillations of the Dirac-cones in the reciprocal space. If the electrons followed adiabatically the Dirac-cone oscillations, no change in the phonon frequency would be observed. Instead, since the electron-momentum relaxation near the Fermi level is much slower than the phonon motion, the electrons do not follow the Dirac-cone displacements. This invalidates BO and results in the observed phonon stiffening. This spectacular failure of BO is quite significant since BO has been the fundamental paradigm to determine crystal vibrations from the early days of quantum mechanics.read more
Citations
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The electronic properties of graphene
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.
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Superior Thermal Conductivity of Single-Layer Graphene
Alexander A. Balandin,Suchismita Ghosh,Wenzhong Bao,Irene Calizo,Desalegne Teweldebrhan,Feng Miao,Chun Ning Lau +6 more
TL;DR: The extremely high value of the thermal conductivity suggests that graphene can outperform carbon nanotubes in heat conduction and establishes graphene as an excellent material for thermal management.
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Graphene and Graphene Oxide: Synthesis, Properties, and Applications
TL;DR: An overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.
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Raman spectroscopy of graphene and graphite: Disorder, electron phonon coupling, doping and nonadiabatic effects
TL;DR: In this article, the authors focus on the origin of the D and G peaks and the second order of D peak and show that the G and 2 D Raman peaks change in shape, position and relative intensity with number of graphene layers.
Journal ArticleDOI
Raman spectroscopy as a versatile tool for studying the properties of graphene
Andrea C. Ferrari,Denis M. Basko +1 more
TL;DR: The state of the art, future directions and open questions in Raman spectroscopy of graphene are reviewed, and essential physical processes whose importance has only recently been recognized are described.
References
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Two-dimensional gas of massless Dirac fermions in graphene
Kostya S. Novoselov,A. K. Geim,Sergey V. Morozov,Da Jiang,Mikhail I. Katsnelson,Irina V. Grigorieva,S. V. Dubonos,A. A. Firsov +7 more
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Journal ArticleDOI
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Andrea C. Ferrari,Jannik C. Meyer,Vittorio Scardaci,Cinzia Casiraghi,Michele Lazzeri,Francesco Mauri,S. Piscanec,Da Jiang,K. S. Novoselov,S. Roth,A. K. Geim +10 more
TL;DR: This work shows that graphene's electronic structure is captured in its Raman spectrum that clearly evolves with the number of layers, and allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area.
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Two-dimensional atomic crystals
Kostya S. Novoselov,Da Jiang,Fred Schedin,Timothy J. Booth,V. V. Khotkevich,Sergey V. Morozov,Andre K. Geim +6 more
TL;DR: By using micromechanical cleavage, a variety of 2D crystals including single layers of boron nitride, graphite, several dichalcogenides, and complex oxides are prepared and studied.
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Raman Spectrum of Graphite
F. Tuinstra,J. L. Koenig +1 more
TL;DR: Raman spectra are reported from single crystals of graphite and other graphite materials as mentioned in this paper, and the Raman intensity of this band is inversely proportional to the crystallite size and is caused by a breakdown of the k-selection rule.
Journal ArticleDOI
Phonons and related crystal properties from density-functional perturbation theory
TL;DR: In this paper, the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method, is reviewed.