13 research outputs found
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From Hopping to Ballistic Transport in Graphene-Based Electronic Devices
This thesis describes electronic transport experiments in graphene from the hopping to the ballistic regime. The first experiment studies dual-gated bilayer graphene devices. By applying an electric field with these dual gates, we can open a band gap in bilayer graphene and observe an increase in resistance of over six orders of magnitude as well as a strongly non-linear behavior in the transport characteristics. A temperature-dependence study of resistance at large electric field at the charge neutrality point shows the change in the transport mechanism from a hopping dominated regime at low temperature to a diffusive regime at high temperature.Physic
Electronic Transport in Dual-gated Bilayer Graphene at Large Displacement Fields
We study the electronic transport properties of dual-gated bilayer graphene
devices. We focus on the regime of low temperatures and high electric
displacement fields, where we observe a clear exponential dependence of the
resistance as a function of displacement field and density, accompanied by a
strong non-linear behavior in the transport characteristics. The effective
transport gap is typically two orders of magnitude smaller than the optical
band gaps reported by infrared spectroscopy studies. Detailed temperature
dependence measurements shed light on the different transport mechanisms in
different temperature regimes.Comment: 4 pages, 3 figure
Quantum Hall Effect, Screening and Layer-Polarized Insulating States in Twisted Bilayer Graphene
We investigate electronic transport in dual-gated twisted bilayer graphene.
Despite the sub-nanometer proximity between the layers, we identify independent
contributions to the magnetoresistance from the graphene Landau level spectrum
of each layer. We demonstrate that the filling factor of each layer can be
independently controlled via the dual gates, which we use to induce Landau
level crossings between the layers. By analyzing the gate dependence of the
Landau level crossings, we characterize the finite inter-layer screening and
extract the capacitance between the atomically-spaced layers. At zero filling
factor, we observe magnetic and displacement field dependent insulating states,
which indicate the presence of counter-propagating edge states with inter-layer
coupling.Comment: 4 pages, 3 figure
BN/Graphene/BN Transistors for RF Applications
In this letter, we demonstrate the first BN/Graphene/BN field effect
transistor for RF applications. The BN/Graphene/BN structure can preserve the
high mobility of graphene, even when it is sandwiched between a substrate and a
gate dielectric. Field effect transistors (FETs) using a bilayer graphene
channel have been fabricated with a gate length LG=450 nm. A current density in
excess of 1 A/mm and DC transconductance close to 250 mS/mm are achieved for
both electron and hole conductions. RF characterization is performed for the
first time on this device structure, giving a current-gain cut-off frequency
fT=33 GHz and an fT.LG product of 15 GHz.um. The improved performance obtained
by the BN/Graphene/BN structure is very promising to enable the next generation
of high frequency graphene RF electronics.Comment: 3 pages, 5 figures, accepted for publication in IEEE Electron Device
Letter
Hot Carrier-Assisted Intrinsic Photoresponse in Graphene
Graphene is a new material showing high promise in optoelectronics,
photonics, and energy-harvesting applications. However, the underlying physical
mechanism of optoelectronic response has not been established. Here, we report
on the intrinsic optoelectronic response of high-quality dual-gated monolayer
and bilayer graphene p-n junction devices. Local laser excitation at the p-n
interface leads to striking six-fold photovoltage patterns as a function of
bottom- and top-gate voltages. These patterns, together with the measured
spatial and density dependence of the photoresponse, provide strong evidence
that non-local hot-carrier transport, rather than the photovoltaic effect,
dominates the intrinsic photoresponse in graphene. This novel regime, which
features a long-lived and spatially distributed hot carrier population, may
open the doorway for optoelectronic technologies exploiting efficient energy
transport at the nanoscale.Comment: 19 pages, 4 figure
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Relaxation and Dephasing in a Two-Electron Nanotube Double Quantum Dot
We use charge sensing of Pauli blockade (including spin and isospin) in a two-electron nanotube double quantum dot to measure relaxation and dephasing times. The relaxation time first decreases with a parallel magnetic field and then goes through a minimum in a field of . We attribute both results to the spin-orbit-modified electronic spectrum of carbon nanotubes, which at high field enhances relaxation due to bending-mode phonons. The inhomogeneous dephasing time is consistent with previous data on hyperfine coupling strength in nanotubes.PhysicsOther Research Uni
Quantum Hall effect and Landau level crossing of Dirac fermions in trilayer graphene
We investigate electronic transport in high mobility (\textgreater 100,000
cm/Vs) trilayer graphene devices on hexagonal boron nitride, which
enables the observation of Shubnikov-de Haas oscillations and an unconventional
quantum Hall effect. The massless and massive characters of the TLG subbands
lead to a set of Landau level crossings, whose magnetic field and filling
factor coordinates enable the direct determination of the
Slonczewski-Weiss-McClure (SWMcC) parameters used to describe the peculiar
electronic structure of trilayer graphene. Moreover, at high magnetic fields,
the degenerate crossing points split into manifolds indicating the existence of
broken-symmetry quantum Hall states.Comment: Supplementary Information at
http://jarilloherrero.mit.edu/wp-content/uploads/2011/04/Supplementary_Taychatanapat.pd
Electrically tunable transverse magnetic focusing in graphene
Author's final manuscript January 9, 2013Electrons in a periodic lattice can propagate without scattering for macroscopic distances despite the presence of the non-uniform Coulomb potential due to the nuclei. Such ballistic motion of electrons allows the use of a transverse magnetic field to focus electrons. This phenomenon, known as transverse magnetic focusing (TMF), has been used to study the Fermi surface of metals and semiconductor heterostructures, as well as to investigate Andreev reflection and spin–orbit interaction, and to detect composite fermions. Here we report on the experimental observation of TMF in high-mobility mono-, bi- and tri-layer graphene devices. The ability to tune the graphene carrier density enables us to investigate TMF continuously from the hole to the electron regime and analyse the resulting focusing fan. Moreover, by applying a transverse electric field to tri-layer graphene, we use TMF as a ballistic electron spectroscopy method to investigate controlled changes in the electronic structure of a material. Finally, we demonstrate that TMF survives in graphene up to 300 K, by far the highest temperature reported for any system, opening the door to new room-temperature applications based on electron-optics.National Science Foundation (U.S.) (CAREER Award DMR-0845287)United States. Office of Naval Research. GATE MURI Projec