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Magneto-optical Selection Rules in Bilayer Bernal Graphene  [PDF]
Yen-Hung Ho,Yu-Huang Chiu,De-Hone Lin,Chen-Peng Chang,Ming-Fa Lin
Physics , 2010, DOI: 10.1021/nn9015339
Abstract: The low-frequency magneto-optical properties of bilayer Bernal graphene are studied by the tight-binding model with four most important interlayer interactions taken into account. Since the main features of the wave functions are well depicted, the Landau levels can be divided into two groups based on the characteristics of the wave functions. These Landau levels lead to four categories of absorption peaks in the optical absorption spectra. Such absorption peaks own complex optical selection rules and these rules can be reasonably explained by the characteristics of the wave functions. In addition, twin-peak structures, regular frequency-dependent absorption rates and complex field-dependent frequencies are also obtained in this work. The main features of the absorption peaks are very different from those in monolayer graphene and have their origin in the interlayer interactions.
Landau Quantization in Graphene Monolayer, Bernal Bilayer, and Bernal Trilayer on Graphite Surface  [PDF]
Long-Jing Yin,Si-Yu Li,Jia-Bin Qiao,Jia-Cai Nie,Lin He
Physics , 2015, DOI: 10.1103/PhysRevB.91.115405
Abstract: Electronic properties of surface areas decoupled from graphite are studied using scanning tunnelling microscopy and spectroscopy. We show that it is possible to identify decoupled graphene monolayer, Bernal bilayer, and Bernal trilayer on graphite surface according to their tunnelling spectra in high magnetic field. The decoupled monolayer and bilayer exhibit Landau quantization of massless and massive Dirac fermions, respectively. The substrate generates a sizable band gap, ~35 meV, in the Bernal bilayer, therefore, the eightfold degenerate Landau level at the charge neutrality point is split into two valley-polarized quartets polarized on each layer. In the decoupled Bernal trilayer, we find that both massless and massive Dirac fermions coexist and its low-energy band structure can be described quite well by taking into account only the nearest-neighbor intra- and interlayer hopping parameters. A strong correlation between the Fermi velocity of the massless Dirac fermions and the effective mass of the massive Dirac fermions is observed in the trilayer. Our result demonstrates that the surface of graphite provides a natural ideal platform to probe the electronic spectra of graphene layers.
Raman spectra of misoriented bilayer graphene  [PDF]
Philippe Poncharal,Anthony Ayari,Thierry Michel,Jean-Louis Sauvajol
Physics , 2008, DOI: 10.1103/PhysRevB.78.113407
Abstract: We compare the main feature of the measured Raman scattering spectra from single layer graphene with a bilayer in which the two layers are arbitrarily misoriented. The profiles of the 2D bands are very similar having only one component, contrary to the four found for commensurate Bernal bilayers. These results agree with recent theoretical calculations and point to the similarity of the electronic structures of single layer graphene and misoriented bilayer graphene. Another new aspect is that the dependance of the 2D frequency on the laser excitation energy is different in these two latter systems.
Magnetic Impurity in Bernal Stacked Bilayer Graphene  [PDF]
J. H. Sun,F. M. Hu,H. K. Tang,H. Q. Lin
Physics , 2012,
Abstract: We investigate a magnetic impurity in Bernal stacked bilayer graphene by a non-perturbative numerical exact approach. In the two cases we study, impurity is placed on the top of two different sublattices (A and B) in bilayer graphene. We find that similar to the monolayer case, magnet moment of the impurity could still be tuned in a wide range through changing the chemical potential. However, the property of the impurity depends strongly on its location due to the broken symmetry between sublattices A and B caused by the Bernal stacking. This difference becomes more apparent with the increase in the hybridization and decrease in the on-site Coulomb repulsion. Additionally, we calculate the impurity spectral densities and the correlation functions between the impurity and the conduction-band electrons. All the computational results show the same spatial dependence on the location of the impurity.
Influence of interlayer asymmetry on magneto-spectroscopy of bilayer graphene  [PDF]
M. Mucha-Kruczynski,E. McCann,V. I. Fal'ko
Physics , 2009, DOI: 10.1016/j.ssc.2009.02.057
Abstract: We present a self-consistent calculation of the interlayer asymmetry in bilayer graphene caused by an applied electric field in magnetic fields. We show how this asymmetry influences the Landau level spectrum in bilayer graphene and the observable inter-Landau level transitions when they are studied as a function of high magnetic field at fixed filling factor as measured experimentally by E.A. Henriksen et al., Phys. Rev. Lett. 100 (2008), 087403. We also analyze the magneto-optical spectra of bilayer flakes in the photon-energy range corresponding to transitions between degenerate and split bands of bilayers.
Phonon and structural changes in deformed Bernal stacked bilayer graphene  [PDF]
Otakar Frank,Milan Bousa,Ibtsam Riaz,Rashid Jalil,Kostya S. Novoselov,Georgia Tsoukleri,John Parthenios,Ladislav Kavan,Konstantinos Papagelis,Costas Galiotis
Physics , 2012, DOI: 10.1021/nl203565p
Abstract: We present the first Raman spectroscopic study of Bernal bilayer graphene flakes under uniaxial tension. Apart from a purely mechanical behavior in flake regions where both layers are strained evenly, certain effects stem from inhomogeneous stress distribution across the layers. These phenomena such as the removal of inversion symmetry in bilayer graphene may have important implications in the band-gap engineering providing an alternative route to induce the formation of a band-gap.
Quantum Hall Effect in Bernal Stacked and Twisted Bilayer Graphene Grown on Cu by Chemical Vapor Deposition  [PDF]
Babak Fallahazad,Yufeng Hao,Kayoung Lee,Seyoung Kim,R. S. Ruoff,E. Tutuc
Physics , 2012, DOI: 10.1103/PhysRevB.85.201408
Abstract: We examine the quantum Hall effect in bilayer graphene grown on Cu substrates by chemical vapor deposition. Spatially resolved Raman spectroscopy suggests a mixture of Bernal (A-B) stacked and rotationally faulted (twisted) domains. Magnetotransport measurements performed on bilayer domains with a wide 2D band reveal quantum Hall states (QHSs) at filling factors $\nu=4, 8, 12$ consistent with a Bernal stacked bilayer, while magnetotransport measurements in bilayer domains defined by a narrow 2D band show a superposition of QHSs of two independent monolayers. The analysis of the Shubnikov-de Haas oscillations measured in twisted graphene bilayers provides the carrier density in each layer as a function of the gate bias and the inter-layer capacitance.
Raman spectra of bilayer graphene to probe the electrostatic environment  [PDF]
Paola Gava,Michele Lazzeri,A. Marco Saitta,Francesco Mauri
Physics , 2009,
Abstract: The Raman shift, broadening, and relative Raman intensities of bilayer graphene are computed as functions of the electron concentration. We include dynamic effects for the phonon frequencies and we consider the gap induced in the band structure of bilayer graphene by an external electric field. We show that from the analysis of the Raman spectra of gated bilayer graphene it is possible to quantitatively identify the amount of charges coming from the atmosphere and from the substrate. These findings suggest that Raman spectroscopy of bilayer graphene can be used to characterize the electrostatic environment of few-layers graphene.
Magneto-optics of monolayer and bilayer graphene  [PDF]
L. A Falkovsky
Physics , 2013, DOI: 10.1134/S0021364013070047
Abstract: The optical conductivity of graphene and bilayer graphene in quantizing magnetic fields is studied. Both dynamical conductivities, longitudinal and Hall's, are analytically evaluated. The conductivity peaks are explained in terms of electron transitions. Correspondences between the transition frequencies and the magneto-optical features are established using the theoretical results. The main optical transitions obey the selection rule with $\Delta n=1$ for the Landau number $n$. The Faraday rotation and light transmission in the quantizing magnetic fields are calculated. The effects of temperatures and magnetic fields on the chemical potential are considered. \pacs{71.20.Nr, 78.20.Ci, 78.20.Bh}
Heating Isotopically Labelled Bernal Stacked Graphene: a Raman Spectroscopy Study  [PDF]
Johan Ek Weis,Sara Costa,Otakar Frank,Martin Kalbac
Physics , 2014, DOI: 10.1021/jz402681n
Abstract: One of the greatest issues of nanoelectronics today is how to control the heating of the components. Graphene is a promising material in this area and it is essential to study its thermal properties. Here, the effect of heating a bilayer structure was investigated using in situ Raman spectroscopy. In order to observe the effects on each individual layer, an isotopically labelled bilayer graphene was synthesized where the two layers are composed of different carbon isotopes. Therefore, the frequency of the phonons in the Raman spectra is shifted in relation to each other. This technique was used to investigate the influence of different stacking order. It was found that in bilayer graphene grown by chemical vapor deposition (CVD) the two layers behave very similarly, for both Bernal stacking and randomly oriented structures, while for transferred samples the layers act more independently. This highlights a significant dependence on sample preparation procedure.
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