23,038 research outputs found
Electrical transport in suspended and double gated trilayer graphene
We present a fabrication process for high quality suspended and double gated
trilayer graphene devices. The electrical transport measurements in these
transistors reveal a high charge carrier mobility (higher than 20000 cm^2/Vs)
and ballistic electric transport on a scale larger than 200nm. We report a
particularly large on/off ratio of the current in ABC-stacked trilayers, up to
250 for an average electric displacement of -0.08 V/nm, compatible with an
electric field induced energy gap. The high quality of these devices is also
demonstrated by the appearance of quantum Hall plateaus at magnetic fields as
low as 500mT.Comment: to appear in Applied Physics Letters. Typos corrected and references
update
Quantum Transport and Band Structure Evolution under High Magnetic Field in Few-Layer Tellurene
Quantum Hall effect (QHE) is a macroscopic manifestation of quantized states
which only occurs in confined two-dimensional electron gas (2DEG) systems.
Experimentally, QHE is hosted in high mobility 2DEG with large external
magnetic field at low temperature. Two-dimensional van der Waals materials,
such as graphene and black phosphorus, are considered interesting material
systems to study quantum transport, because it could unveil unique host
material properties due to its easy accessibility of monolayer or few-layer
thin films at 2D quantum limit. Here for the first time, we report direct
observation of QHE in a novel low-dimensional material system:
tellurene.High-quality 2D tellurene thin films were acquired from recently
reported hydrothermal method with high hole mobility of nearly 3,000 cm2/Vs at
low temperatures, which allows the observation of well-developed
Shubnikov-de-Haas (SdH) oscillations and QHE. A four-fold degeneracy of Landau
levels in SdH oscillations and QHE was revealed. Quantum oscillations were
investigated under different gate biases, tilted magnetic fields and various
temperatures, and the results manifest the inherent information of the
electronic structure of Te. Anomalies in both temperature-dependent oscillation
amplitudes and transport characteristics were observed which are ascribed to
the interplay between Zeeman effect and spin-orbit coupling as depicted by the
density functional theory (DFT) calculations
Observation of Valley Zeeman and Quantum Hall Effects at Q Valley of Few-Layer Transition Metal Disulfides
In few-layer (FL) transition metal dichalcogenides (TMDC), the conduction
bands along the Gamma-K directions shift downward energetically in the presence
of interlayer interactions, forming six Q valleys related by three-fold
rotational symmetry and time reversal symmetry. In even-layers the extra
inversion symmetry requires all states to be Kramers degenerate, whereas in
odd-layers the intrinsic inversion asymmetry dictates the Q valleys to be
spin-valley coupled. In this Letter, we report the transport characterization
of prominent Shubnikov-de Hass (SdH) oscillations for the Q valley electrons in
FL transition metal disulfide (TMDs), as well as the first quantum Hall effect
(QHE) in TMDCs. Our devices exhibit ultrahigh field-effect mobilities (~16,000
cm2V-1s-1 for FL WS2 and ~10,500 cm2V-1s-1 for FL MoS2) at cryogenic
temperatures. Universally in the SdH oscillations, we observe a valley Zeeman
effect in all odd-layer TMD devices and a spin Zeeman effect in all even-layer
TMD devices.Comment: 20 pages, 4 figure
A capacitance spectroscopy-based platform for realizing gate-defined electronic lattices
Electrostatic confinement in semiconductors provides a flexible platform for
the emulation of interacting electrons in a two-dimensional lattice, including
in the presence of gauge fields. This combination offers the potential to
realize a wide host of quantum phases. Here we present a measurement and
fabrication scheme that builds on capacitance spectroscopy and allows for the
independent control of density and periodic potential strength imposed on a
two-dimensional electron gas. We characterize disorder levels and
(in)homogeneity and develop and optimize different gating strategies at length
scales where interactions are expected to be strong. A continuation of these
ideas might see to fruition the emulation of interaction-driven Mott
transitions or Hofstadter butterfly physics
Scale-invariant large nonlocality in polycrystalline graphene
The observation of large nonlocal resistances near the Dirac point in
graphene has been related to a variety of intrinsic Hall effects, where the
spin or valley degrees of freedom are controlled by symmetry breaking
mechanisms. Engineering strong spin or valley Hall signals on scalable graphene
devices could stimulate further practical developments of spin- and
valleytronics. Here we report on scale-invariant nonlocal transport in
large-scale chemical vapour deposition graphene under an applied external
magnetic field. Contrary to previously reported Zeeman spin Hall effect, our
results are explained by field-induced spin-filtered edge states whose
sensitivity to grain boundaries manifests in the nonlocal resistance. This
phenomenon, related to the emergence of the quantum Hall regime, persists up to
the millimeter scale, showing that polycrystalline morphology can be imprinted
in nonlocal transport. This suggests that topological Hall effects in
large-scale graphene materials are highly sensitive to the underlying
structural morphology, limiting practical realizations.Comment: Main paper (14 pages, 5 figures) and Supplementary information (8
pages, 8 figures
Broken symmetry states and divergent resistance in suspended bilayer graphene
Graphene [1] and its bilayer have generated tremendous excitement in the
physics community due to their unique electronic properties [2]. The intrinsic
physics of these materials, however, is partially masked by disorder, which can
arise from various sources such as ripples [3] or charged impurities [4].
Recent improvements in quality have been achieved by suspending graphene flakes
[5,6], yielding samples with very high mobilities and little charge
inhomogeneity. Here we report the fabrication of suspended bilayer graphene
devices with very little disorder. We observe fully developed quantized Hall
states at magnetic fields of 0.2 T, as well as broken symmetry states at
intermediate filling factors , , and . The
devices exhibit extremely high resistance in the state that grows
with magnetic field and scales as magnetic field divided by temperature. This
resistance is predominantly affected by the perpendicular component of the
applied field, indicating that the broken symmetry states arise from many-body
interactions.Comment: 23 pages, including 4 figures and supplementary information; accepted
to Nature Physic
Quantum transport in double-gated graphene devices
Double-gated graphene devices provide an important platform for understanding
electrical and optical properties of graphene. Here we present transport
measurements of single layer, bilayer and trilayer graphene devices with
suspended top gates. In zero magnetic fields, we observe formation of pnp
junctions with tunable polarity and charge densities, as well as a tunable band
gap in bilayer graphene and a tunable band overlap in trilayer graphene. In
high magnetic fields, the devices' conductance are quantized at integer and
fractional values of conductance quantum, and the data are in good agreement
with a model based on edge state equilibration at pn interfaces
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