1,891 research outputs found
Landau level spectroscopy of ultrathin graphite layers
Far infrared transmission experiments are performed on ultrathin epitaxial
graphite samples in a magnetic field. The observed cyclotron resonance-like and
electron-positron-like transitions are in excellent agreement with the
expectations of a single-particle model of Dirac fermions in graphene, with an
effective velocity of c* = 1.03 x 10^6 m/s.Comment: 4 pages 4 figures Slight revisions following referees' comments. One
figure modifie
Few layer graphene on SiC, pyrolitic graphite and graphene: a Raman scattering study
The results of micro-Raman scattering measurements performed on three
different ``graphitic'' materials: micro-structured disks of highly oriented
pyrolytic graphite, graphene multi-layers thermally decomposed from carbon
terminated surface of 4H-SiC and an exfoliated graphene monolayer are
presented. Despite its multi-layer character, most parts of the surface of the
graphitized SiC substrates shows a single-component, Lorentzian shape, double
resonance Raman feature in striking similarity to the case of a single graphene
monolayer. Our observation suggests a very weak electronic coupling between
graphitic layers on the SiC surface, which therefore can be considered to be
graphene multi-layers with a simple (Dirac-like) band structure.Comment: 4 pages, 3 Figures Structure of the paper strongly modified, small
changes in Fig 2 and 3. Same interpretation and same result
Experimental observation of nanoscale radiative heat flow due to surface plasmons in graphene and doped silicon
Owing to its two dimensional electronic structure, graphene exhibits many
unique properties. One of them is a wave vector and temperature dependent
plasmon in the infrared range. Theory predicts that due to these plasmons,
graphene can be used as a universal material to enhance nanoscale radiative
heat exchange for any dielectric substrate. Here we report on radiative heat
transfer experiments between SiC and a SiO2 sphere which have non matching
phonon polariton frequencies, and thus only weakly exchange heat in near field.
We observed that the heat flux contribution of graphene epitaxially grown on
SiC dominates at short distances. The influence of plasmons on radiative heat
transfer is further supported with measurements for doped silicon. These
results highlight graphenes strong potential in photonic nearfield and energy
conversion devices.Comment: 4 pages, 3 figure
In situ imaging of field emission from individual carbon nanotubes and their structural damage
©2002 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?APPLAB/80/856/1DOI:10.1063/1.1446994Field emission of individual carbon nanotubes was observed by in situ
transmission electron microscopy. A fluctuation in emission current was due to a
variation in distance between the nanotube tip and the counter electrode owing
to a "head-shaking" effect of the nanotube during field emission. Strong
field-induced structural damage of a nanotube occurs in two ways: a
piece-by-piece and segment-by-segment pilling process of the graphitic layers,
and a concentrical layer-by-layer stripping process. The former is believed
owing to a strong electrostatic force, and the latter is likely due to heating
produced by emission current that flowed through the most outer graphitic
layers
Weak antilocalization in epitaxial graphene: evidence for chiral electrons
Transport in ultrathin graphite grown on silicon carbide is dominated by the
electron-doped epitaxial layer at the interface. Weak anti-localization in 2D
samples manifests itself as a broad cusp-like depression in the longitudinal
resistance for magnetic fields 10 mT 5 T. An extremely sharp
weak-localization resistance peak at B=0 is also observed. These features
quantitatively agree with graphene weak-(anti)localization theory implying the
chiral electronic character of the samples. Scattering contributions from the
trapped charges in the substrate and from trigonal warping due to the graphite
layer on top are tentatively identified. The Shubnikov-de Haas oscillations are
remarkably small and show an anomalous Berry's phase.Comment: 5 pages, 4 figures. Minor change
Plasmon assisted transport through disordered array of quantum wires
Phononless plasmon assisted thermally activated transport through a long
disordered array of finite length quantum wires is investigated analytically.
Generically strong electron plasmon interaction in quantum wires results in a
qualitative change of the temperature dependence of thermally activated
resistance in comparison to phonon assisted transport. At high temperatures,
the thermally activated resistance is determined by the Luttinger liquid
interaction parameter of the wires.Comment: 7 pages, 1 figure, final version as publishe
Resonant Excitation of Graphene K-Phonon and Intra-Landau-Level Excitons in Magneto-Optical Spectroscopy
Precise infrared magnetotransmission experiments have been performed in
magnetic fields up to 32 T on a series of multilayer epitaxial graphene
samples. We observe changes in the spectral features and broadening of the main
cyclotron transition when the incoming photon energy is in resonance with the
lowest Landau level separation and the energy of a K point optical phonon. We
have developed a theory that explains and quantitatively reproduces the
frequency and magnetic field dependence of the phenomenon as the absorption of
a photon together with the simultaneous creation of an intervalley,
intra-Landau-level exciton, and a K phonon.Comment: Main manuscript (5 pages); Supplementary Material (18 pages
Magnetoplasmons in quasi-neutral epitaxial graphene nanoribbons
We present infrared transmission spectroscopy study of the inter-Landau-level
excitations in quasi-neutral epitaxial graphene nanoribbon arrays. We observed
a substantial deviation in energy of the transition
from the characteristic square root magnetic-field dependence of
two-dimensional graphene. This deviation arises from the formation of
upper-hybrid mode between the Landau level transition and the plasmon
resonance. In the quantum regime the hybrid mode exhibits a distinct dispersion
relation, markedly different from that expected for conventional
two-dimensional systems and highly doped graphene
Tuning the electron-phonon coupling in multilayer graphene with magnetic fields
Magneto Raman scattering study of the E optical phonons in multi-layer
epitaxial graphene grown on a carbon face of SiC are presented. At 4.2K 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 E 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.Comment: 4 pages, 3 figure
Effect of a magnetic field on the two-phonon Raman scattering in graphene
We have studied, both experimentally and theoretically, the change of the
so-called 2D band of the Raman scattering spectrum of graphene (the two-phonon
peak near 2700 cm-1) in an external magnetic field applied perpendicular to the
graphene crystal plane at liquid helium temperature. A shift to lower frequency
and broadening of this band is observed as the magnetic field is increased from
0 to 33 T. At fields up to 5--10 T the changes are quadratic in the field while
they become linear at higher magnetic fields. This effect is explained by the
curving of the quasiclassical trajectories of the photo-excited electrons and
holes in the magnetic field, which enables us (i) to extract the electron
inelastic scattering rate, and (ii) to conclude that electronic scattering
accounts for about half of the measured width of the 2D peak.Comment: 11 pages, 7 figure
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