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ABSTRACT: The electronic structure of Bernal-stacked graphite subject to tilted
magnetic fields has been investigated using infrared magneto-transmission
experiments. With the increasing in-plane component of the magnetic field B, we
observe significant broadening and partially also splitting of interband
inter-Landau level transitions, which originate at the H point of the graphite
Brillouin zone, where the charge carriers behave as massless Dirac fermions.
The observed behavior is attributed to the lifting of the twofold degeneracy of
Landau levels at the H point - a degeneracy which in graphite complements the
standard spin and valley degeneracies typical of graphene.
08/2012;
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ABSTRACT: Polarization resolved, Raman scattering response due to E$_{2g}$ phonon in
monolayer graphene has been investigated in magnetic fields up to 29 T. The
hybridization of the E$_{2g}$ phonon with only the fundamental inter Landau
level excitation (involving the n=0 Landau level) is observed and only in one
of the two configurations of the circularly crossed polarized excitation and
scattered light. This polarization anisotropy of the magneto-phonon resonance
is shown to be inherent to relatively strongly doped graphene samples, with
carrier concentration typical for graphene deposited on SiO$_2$.
07/2012;
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ABSTRACT: We show how the magneto-phonon resonance, particularly pronounced in sp2
carbon allotropes, can be used as a tool to probe the band structure of
multilayer graphene specimens. Even when electronic excitations cannot be
directly observed, their coupling to the E2g phonon leads to pronounced
oscillations of the phonon feature observed through Raman scattering
experiments with multiple periods and amplitudes detemined by the electronic
excitation spectrum. Such experiment and analysis have been performed up to 28T
on an exfoliated 4-layer graphene specimen deposited on SiO2, and the observed
oscillations correspond to the specific AB stacked 4-layer graphene electronic
excitation spectrum.
06/2012;
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ABSTRACT: We report on absolute magneto-transmission experiments on highly-doped
quasi-free-standing epitaxial graphene targeting the classical-to-quantum
crossover of the cyclotron resonance. This study allows us to directly extract
the carrier density and also other relevant quantities such as the
quasiparticle velocity and the Drude weight, which is precisely measured from
the strength of the cyclotron resonance. We find that the Drude weight is
renormalized with respect to its non-interacting (or
random-phase-approximation) value and that the renormalization is tied to the
quasiparticle velocity enhancement. This finding is in agreement with recent
theoretical predictions, which attribute the renormalization of the Drude
weight in graphene to the interplay between broken Galilean invariance and
electron-electron interactions.
05/2012;
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ABSTRACT: The micro-Raman scattering response of a graphene-like location on the
surface of bulk natural graphite is investigated both at $T=\unit{4.2}{K}$ and
at room temperature in magnetic fields up to 29 T. Two different polarization
configurations, co-circular and crossed-circular, are employed in order to
determine the Raman scattering selection rules. Several distinct series of
electronic excitations are observed and we discuss their characteristic shapes
and amplitudes. In particular, we report a clear splitting of the signals
associated with the inter-Landau level excitations $-n\rightarrow+n$.
Furthermore, we observe the pronounced interaction of the zone-center
E$_{\text{2g}}$-phonon with three different sets of electronic excitations.
Possible origins for these graphene-like inclusions on the surface of bulk
graphite are discussed.
03/2012;
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ABSTRACT: Graphite, a model (semi)metal with trigonally warped bands, is investigated with a magnetoabsorption experiment and viewed as an electronic system in the vicinity of the Lifshitz transition. A characteristic pattern of up to 20 cyclotron resonance harmonics has been observed. This large number of resonances, their relative strengths and characteristic shapes trace the universal properties of the electronic states near a separatrix in momentum space. Quantum-mechanical perturbative methods with respect to the trigonal warping term hardly describe the data which are, on the other hand, fairly well reproduced within a quasiclassical approach and conventional band structure model. Trigonal symmetry is preserved in graphite in contrast to a similar system, bilayer graphene.
Physical Review Letters 01/2012; 108(1):017602. · 7.37 Impact Factor
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ABSTRACT: The energy dependence of the electronic scattering time is probed by Landau level spectroscopy in quasineutral multilayer epitaxial graphene. From the broadening of overlapping Landau levels we find that the scattering rate 1/τ increases linearly with energy ϵ. This implies a surprising property of the Landau level spectrum in graphene-the number of resolved Landau levels remains constant with the applied magnetic field. Insights are given about possible scattering mechanisms and carrier mobilities in the graphene system investigated.
Physical Review Letters 11/2011; 107(21):216603. · 7.37 Impact Factor
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ABSTRACT: We use polarized magneto-Raman scattering to study purely electronic
excitations and the electron-phonon coupling in bulk graphite. At a temperature
of 4.2 K and in magnetic fields up to 28 T we observe $K$-point electronic
excitations involving Landau bands with $\Delta |n|=0$ and with $\Delta
|n|=\pm2$ that can be selected by controlling the angular momentum of the
excitation laser and of the scattered light. The magneto-phonon effect
involving the $E_{2g}$ optical phonon and $K$-point inter Landau bands
electronic excitations with $\Delta |n|=\pm1$ is revealed and analyzed within a
model taking into account the full $k_z$ dispersion. These polarization
resolved results are explained in the frame of the Slonczewski-Weiss-McClure
(SWM) model which directly allows to quantify the electron-hole asymmetry.
10/2011;
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ABSTRACT: Magneto-Raman-scattering experiments from the surface of graphite reveal novel features associated to purely electronic excitations which are observed in addition to phonon-mediated resonances. Graphene-like and graphite domains are identified through experiments with ∼1 μm spatial resolution performed in magnetic fields up to 32 T. Polarization resolved measurements emphasize the characteristic selection rules for electronic transitions in graphene. Graphene on graphite displays the unexpected hybridization between optical phonon and symmetric across the Dirac point inter Landau level transitions. The results open new experimental possibilities--to use light scattering methods in studies of graphene under quantum Hall effect conditions.
Physical Review Letters 07/2011; 107(3):036807. · 7.37 Impact Factor
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ABSTRACT: The energy-dependence of the electronic scattering time is probed by Landau
level spectroscopy in quasi neutral multilayer epitaxial graphene. From the
Landau levels broadening we find that the scattering rate increases linearly
with energy. This implies a surprising property of the Landau level spectrum in
graphene - the number of the resolved Landau levels remains constant with the
applied magnetic field. Insights are given about possible scattering mechanism
and carrier mobilities in the graphene system investigated.
01/2011;
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ABSTRACT: HgTe/HgCdTe quantum wells with the inverted band structure have been probed
using far infrared magneto-spectroscopy. Realistic calculations of Landau level
diagrams have been performed to identify the observed transitions.
Investigations have been greatly focused on the magnetic field dependence of
the peculiar pair of "zero-mode" Landau levels which characteristically split
from the upper conduction and bottom valence bands, and merge under the applied
magnetic field. The observed avoided crossing of these levels is tentatively
attributed to the bulk inversion asymmetry of zinc blend compounds.
11/2010;
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ABSTRACT: Precise absolute far–infra-red magneto-transmission experiments have been performed under magnetic fields up to 28T on a series of single Ga0.24In0.76As quantum wells n-type modulation doped at different levels. The transmission spectra have been simulated with a multilayer dielectric model. This allows us to extract the imaginary part of the optical response function which reveals new singular features related to electron-phonon interactions. In addition to the expected polaronic effects due to the longitudinal (LO) phonons, one observes other interactions with the transverse optical (TO) phonons and a new kind of carrier concentrationdependent interaction with interface phonons. This system provides a unique opportunity to study multiple types of electron-phonon interactions in a single type of compound. yes yes
EPL (Europhysics Letters) 11/2010; · 2.17 Impact Factor
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M. Orlita, C. Faugeras,
J. Borysiuk,
J. M. Baranowski,
W. Strupinski,
M. Sprinkle,
C. Berger,
W. A. de Heer,
D. M. Basko,
G Martinez,
M. Potemski
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ABSTRACT: Additional component in multi-layer epitaxial graphene grown on the
C-terminated surface of SiC, which exhibits the characteristic electronic
properties of a AB-stacked graphene bilayer, is identified in magneto-optical
response of this material. We show that these inclusions represent a
well-defined platform for accurate magneto-spectroscopy of unperturbed graphene
bilayers.
Physical review. B, Condensed matter 10/2010; 83(12).
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ABSTRACT: Cyclotron resonance in highly doped graphene has been explored using infrared magnetotransmission. Contrary to previous work, which only focused on the magneto-optical properties of graphene in the quantum regime, here we study the quasiclassical response of this system. We show that it has a character of classical cyclotron resonance, with an energy which is linear in the applied magnetic field and with an effective cyclotron mass defined by the position of the Fermi level m=EF/vF2.
Phys. Rev. B. 10/2010; 82(16).
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ABSTRACT: Magneto-Raman scattering study of the E2g optical phonons in multilayer epitaxial graphene grown on a carbon face of SiC is presented. At 4.2 K in magnetic field up to 33 T, we observe a series of well-pronounced avoided crossings each time the optically active inter-Landau level transition is tuned in resonance with the E2g phonon excitation (at 196 meV). The width of the phonon Raman scattering response also shows pronounced variations and is enhanced in conditions of resonance. The experimental results are well reproduced by a model that gives directly the strength of the electron-phonon interaction.
Physical Review Letters 10/2009; 103(18):186803. · 7.37 Impact Factor
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ABSTRACT: Precise absolute far-infra-red magneto-transmission experiments have been performed in magnetic fields up to 33 T on a series of single GaAs quantum wells doped at different levels. The transmission spectra have been simulated with a multilayer dielectric model. The imaginary part of the optical response function which reveals new singular features related to the electron-phonon interactions has been extracted. In addition to the expected polaronic effects due to the longitudinal optical (LO) phonon of GaAs, a new kind of carrier concentration dependent interaction with interface phonons is observed. A simple physical model is used to try to quantify these interactions and explore their origin. Comment: 4 pages, 2 Figures
09/2009;
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ABSTRACT: We have identified the cyclotron resonance response of the purest graphene ever investigated, which can be found in nature on the surface of bulk graphite, in the form of decoupled layers from the substrate material. Probing such flakes with Landau level spectroscopy in the THz range at very low magnetic fields, we demonstrate a superior electronic quality of these ultralow density layers (n_{0} approximately 3 x 10;{9} cm;{-2}) expressed by the carrier mobility in excess of 10;{7} cm;{2}/(V * s) or scattering time of tau approximately 20 ps. These parameters set new and surprisingly high limits for intrinsic properties of graphene and represent an important challenge for further developments of current graphene technologies.
Physical Review Letters 09/2009; 103(13):136403. · 7.37 Impact Factor
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ABSTRACT: We describe an infrared transmission study of a thin layer of bulk graphite in magnetic fields up to B=34 T. Two series of absorption lines whose energy scales as sqrt[B] and B are present in the spectra and identified as contributions of massless holes at the H point and massive electrons in the vicinity of the K point, respectively. We find that the optical response of the K point electrons corresponds, over a wide range of energy and magnetic field, to a graphene bilayer with an effective interlayer coupling 2gamma_{1}, twice the value for a real graphene bilayer, which reflects the crystal ordering of bulk graphite along the c axis. The K point electrons thus behave as massive Dirac fermions with a mass enhanced twice in comparison to a true graphene bilayer.
Physical Review Letters 05/2009; 102(16):166401. · 7.37 Impact Factor
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M Orlita, C Faugeras,
P Plochocka,
P Neugebauer,
G Martinez,
D K Maude,
A L Barra,
M Sprinkle,
C Berger,
W A de Heer,
M Potemski
[show abstract]
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ABSTRACT: Multilayer epitaxial graphene is investigated using far infrared transmission experiments in the different limits of low magnetic fields and high temperatures. The cyclotron-resonance-like absorption is observed at low temperature in magnetic fields below 50 mT, probing the nearest vicinity of the Dirac point. The carrier mobility is found to exceed 250,000 cm2/(V x s). In the limit of high temperatures, the well-defined Landau level quantization is observed up to room temperature at magnetic fields below 1 T, a phenomenon unusual in solid state systems. A negligible increase in the width of the cyclotron resonance lines with increasing temperature indicates that no important scattering mechanism is thermally activated.
Physical Review Letters 01/2009; 101(26):267601. · 7.37 Impact Factor
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ABSTRACT: The magneto-transmission of a thin layer of bulk graphite is compared with spectra taken on multi-layer epitaxial graphene prepared by thermal decomposition of a SiC crystal. We focus on the spectral features evolving as , which are evidence for the presence of Dirac fermions in both materials. Whereas the results on multi-layer epitaxial graphene can be interpreted within the model of 2D Dirac fermions, the data obtained on bulk graphite can only be explained taking into account the 3D nature of graphite, e.g. by using the standard Slonczewski–Weiss–McClure model.
Solid State Communications. 10/2008;
