91 research outputs found
High magnetic field induced charge density waves and sign reversal of the Hall coefficient in graphite
We report on the investigation of magnetic field induced charge density wave
and Hall coefficient sign reversal in a quasi-two dimensional electronic system
of highly oriented pyrolytic graphite under very strong magnetic field. The
change of Hall sign coefficient from negative to positive occurs at low
temperature and high magnetic field just after the charge density wave
transition, suggesting the role of hole-like quasi-particles in this effect.
Angular dependent measurements show that the charge density wave transition and
Hall sign reversal fields follow the magnetic field component along the c-axis
of graphite
Electron-hole coexistence in disordered graphene probed by high-field magneto-transport
We report on magneto-transport measurement in disordered graphene under
pulsed magnetic field of up to 57T. For large electron or hole doping, the
system displays the expected anomalous Integer Quantum Hall Effect (IQHE)
specific to graphene up to filling factor . In the close vicinity of the
charge neutrality point, the system breaks up into co-existing puddles of holes
and electrons, leading to a vanishing Hall and finite longitudinal resistance
with no hint of divergence at very high magnetic field. Large resistance
fluctuations are observed near the Dirac point. They are interpreted as the the
natural consequence of the presence of electron and hole puddles. The magnetic
field at which the amplitude of the fluctuations are the largest is directly
linked to the mean size of the puddles
Edge Magneto-Fingerprints in Disordered Graphene Nanoribbons
We report on (magneto)-transport experiments in chemically derived narrow
graphene nanoribbons under high magnetic fields (up to 60 Tesla). Evidences of
field-dependent electronic confinement features are given, and allow estimating
the possible ribbon edge symmetry. Besides, the measured large positive
magnetoconductance indicates a strong suppression of backscattering induced by
the magnetic field. Such scenario is supported by quantum simulations which
consider different types of underlying disorders (smooth edge disorder and long
range Coulomb scatters).Comment: 4 pages, 4 figure
Integer Quantum Hall Effect in Trilayer Graphene
The Integer Quantum Hall Effect (IQHE) is a distinctive phase of
two-dimensional electronic systems subjected to a perpendicular magnetic field.
Thus far, the IQHE has been observed in semiconductor heterostructures and in
mono- and bi-layer graphene. Here we report on the IQHE in a new system:
trilayer graphene. Experimental data are compared with self-consistent Hartree
calculations of the Landau levels for the gated trilayer. The plateau structure
in the Hall resistivity determines the stacking order (ABA versus ABC). We find
that the IQHE in ABC trilayer graphene is similar to that in the monolayer,
except for the absence of a plateau at filling factor v=2. At very low filling
factor, the Hall resistance vanishes due to the presence of mixed electron and
hole carriers induced by disorder.Comment: 5 pages, 4 figure
High sensitivity variable-temperature infrared nanoscopy of conducting oxide interfaces
Probing the local transport properties of two-dimensional electron systems
(2DES) confined at buried interfaces requires a non-invasive technique with a
high spatial resolution operating in a broad temperature range. In this paper,
we investigate the scattering-type scanning near field optical microscopy as a
tool for studying the conducting LaAlO3/SrTiO3 interface from room temperature
down to 6 K. We show that the near-field optical signal, in particular its
phase component, is highly sensitive to the transport properties of the
electron system present at the interface. Our modelling reveals that such
sensitivity originates from the interaction of the AFM tip with coupled
plasmon-phonon modes with a small penetration depth. The model allows us to
quantitatively correlate changes in the optical signal with the variation of
the 2DES transport properties induced by cooling and by electrostatic gating.
To probe the spatial resolution of the technique, we image conducting
nano-channels written in insulating heterostructures with a voltage-biased tip
of an atomic force microscope.Comment: 19 pages, 5 figure
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
Directional silicon nano-antennas for quantum emitter control designed by evolutionary optimization
We optimize silicon nano-antennas to enhance and steer the emission of local
quantum sources. We combine global evolutionary optimization (EO) with
frequency domain electrodynamical simulations, and compare design strategies
based on resonant and non-resonant building blocks. Specifically, we
investigate the performance of models with different degrees of freedom but
comparable amount of available material. We find that simpler geometric models
allow significantly faster convergence of the optimizer, which, expectedly,
comes at the cost of a reduced optical performance. We finally analyze the
physical mechanisms underlying the directional emission that also comes with an
emission rate enhancement, and find a surprising robustness against
perturbations of the source emitter location. This makes the structures highly
interesting for actual nano-fabrication. We believe that optimized,
all-dielectric silicon nano-antennas have high potential for genuine
breakthroughs in a multitude of applications in nanophotonics and quantum
technologies.Comment: 8 pages, 6 figure
- …