2,997 research outputs found
Wave packet revivals in a graphene quantum dot in a perpendicular magnetic field
We study the time-evolution of localized wavepackets in graphene quantum dots
under a perpendicular magnetic field, focusing on the quasiclassical and
revival periodicities, for different values of the magnetic field intensities
in a theoretical framework. We have considered contributions of the two
inequivalent points in the Brillouin zone. The revival time has been found as
an observable that shows the break valley degeneracy.Comment: 5 pages, 4 figures, corrected typo, To appear in Phys. Rev.
Theory of Weiss oscillations in the magnetoplasmon spectrum of Dirac electrons in graphene
We present the collective excitations spectrum (magnetoplasmon spectrum) of
Dirac electrons in a weakly modulated single graphene layer in the presence
of a uniform magnetic field. We consider electric modulation in one-dimension
and the magnetic field applied perpendicular to graphene.We derive analytical
results for the intra-Landau band plasmon spectrum within the
self-consistent-field approach. We find Weiss oscillations in the
magnetoplasmon spectrum which is the primary focus of this work. Results are
presented for the intra-Landau band magnetoplasmon spectrum as a function of
inverse magnetic field. These results are also compared with those of
conventional 2DEG. We have found that the Weiss oscillations in the
magnetoplasmon spectrum are larger in amplitude compared to those in
conventional 2DEG for the same modulation strength, period of modulation and
electron density.Comment: 9 pages, 1 figure Phys. Rev. B (accepted for publication
Unconventional quantum Hall effect and Berry’s phase 2pi in bilayer graphene.
There are known two distinct types of the integer quantum Hall effect. One is the conventional quantum Hall effect, characteristic of two-dimensional semiconductor systems, and the other is its relativistic counterpart recently observed in graphene, where charge carriers mimic Dirac fermions characterized by Berry’s phase pi, which results in a shifted positions of Hall plateaus. Here we report a third type of the integer quantum Hall effect. Charge carriers in bilayer graphene have a parabolic energy spectrum but are chiral and exhibit Berry’s phase 2pi affecting their quantum dynamics. The Landau quantization of these fermions results in plateaus in Hall conductivity at standard integer positions but the last (zero-level) plateau is missing. The zero-level anomaly is accompanied by metallic conductivity in the limit of low concentrations and high magnetic fields, in stark contrast to the conventional, insulating behavior in this regime. The revealed chiral fermions have no known analogues and present an intriguing case for quantum-mechanical studies
Giant Intrinsic Carrier Mobilities in Graphene and Its Bilayer
We have studied temperature dependences of electron transport in graphene and
its bilayer and found extremely low electron-phonon scattering rates that set
the fundamental limit on possible charge carrier mobilities at room
temperature. Our measurements have shown that mobilities significantly higher
than 200,000 cm2/Vs are achievable, if extrinsic disorder is eliminated. A
sharp (threshold-like) increase in resistivity observed above approximately
200K is unexpected but can qualitatively be understood within a model of a
rippled graphene sheet in which scattering occurs on intra-ripple flexural
phonons
Inter-band magnetoplasmons in mono- and bi-layer graphene
Collective excitations spectrum of Dirac electrons in mono and bilayer
graphene in the presence of a uniform magnetic field is investigated.
Analytical results for inter-Landau band plasmon spectrum within the
self-consistent-field approach are obtained. SdH type oscillations that are a
monotonic function of the magnetic field are observed in the plasmon spectrum
of both mono- and bi-layer graphene systems. The results presented are also
compared with those obtained in conventional 2DEG. The chiral nature of the
quasiparticles in mono and bilayer graphene system results in the observation
of and Berry's phase in the SdH- type oscillations in the plasmon
spectrum.Comment: 9 pages, 2 figure
Generating quantizing pseudomagnetic fields by bending graphene ribbons
We analyze the mechanical deformations that are required to create uniform pseudomagnetic fields in graphene. It is shown that, if a ribbon is bent in-plane into a circular arc, this can lead to fields exceeding 10 T, which is sufficient for the observation of pseudo-Landau quantization. The arc geometry is simpler than those suggested previously and, in our opinion, has much better chances to be realized experimentally soon. The effects of a scalar potential induced by dilatation in this geometry is shown to be negligible.F.G. acknowledges support from MICINN Spain
through Grants No. FIS2008-00124 and No. CONSOLIDER
CSD2007-00010, and by the Comunidad de Madrid, through
CITECNOMIK. M.I.K. acknowledges support from FOM
the Netherlands. This work was also supported by EPSRC
U.K., ONR, AFOSR, and the Royal Society. We are thankful
to Y.-W. Son for useful insights concerning Ref. 17 and
related work.Peer reviewe
Electric Field Effect in Atomically Thin Carbon Films
We report a naturally-occurring two-dimensional material (graphene that can
be viewed as a gigantic flat fullerene molecule, describe its electronic
properties and demonstrate all-metallic field-effect transistor, which uniquely
exhibits ballistic transport at submicron distances even at room temperature
Density of states and zero Landau level probed through capacitance of graphene
We report capacitors in which a finite electronic compressibility of graphene
dominates the electrostatics, resulting in pronounced changes in capacitance as
a function of magnetic field and carrier concentration. The capacitance
measurements have allowed us to accurately map the density of states D, and
compare it against theoretical predictions. Landau oscillations in D are robust
and zero Landau level (LL) can easily be seen at room temperature in moderate
fields. The broadening of LLs is strongly affected by charge inhomogeneity that
leads to zero LL being broader than other levels
Gap opening in the zeroth Landau level of graphene
We have measured a strong increase of the low-temperature resistivity
and a zero-value plateau in the Hall conductivity at
the charge neutrality point in graphene subjected to high magnetic fields up to
30 T. We explain our results by a simple model involving a field dependent
splitting of the lowest Landau level of the order of a few Kelvin, as extracted
from activated transport measurements. The model reproduces both the increase
in and the anomalous plateau in in terms of
coexisting electrons and holes in the same spin-split zero-energy Landau level.Comment: 4 pages, 3 figure
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