805 research outputs found
Interaction-induced shift of the cyclotron resonance of graphene using infrared spectroscopy
We report a study of the cyclotron resonance (CR) transitions to and from the
unusual Landau level (LL) in monolayer graphene. Unexpectedly, we find
the CR transition energy exhibits large (up to 10%) and non-monotonic shifts as
a function of the LL filling factor, with the energy being largest at
half-filling of the level. The magnitude of these shifts, and their
magnetic field dependence, suggests that an interaction-enhanced energy gap
opens in the level at high magnetic fields. Such interaction effects
normally have limited impact on the CR due to Kohn's theorem [W. Kohn, Phys.
Rev. {\bf 123}, 1242 (1961)], which does not apply in graphene as a consequence
of the underlying linear band structure.Comment: 4 pages, 4 figures. Version 2, edited for publication. Includes a
number of edits for clarity; also added a paragraph contrasting our work w/
previous CR expts. in 2D Si and GaA
Infrared spectroscopy of Landau levels in graphene
We report infrared studies of the Landau level (LL) transitions in single
layer graphene. Our specimens are density tunable and show \textit{in situ}
half-integer quantum Hall plateaus. Infrared transmission is measured in
magnetic fields up to B=18 T at selected LL fillings. Resonances between hole
LLs and electron LLs, as well as resonances between hole and electron LLs are
resolved. Their transition energies are proportional to and the
deduced band velocity is m/s. The lack of
precise scaling between different LL transitions indicates considerable
contributions of many-particle effects to the infrared transition energies.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
INSTRUCTIONAL DESIGN AND ASSESSMENT Electronic Integration of Prerequisite Course Content
Objectives. To evaluate the effect of electronic integration of embedded prerequisite information (EPI) on student learning. Design. Specific prerequisite information presented in a Chemical Basis of Drug Action course and important to understanding new topics presented in subsequent courses was identified and embedded in online course materials using pop-ups and hyperlinks. Students were encouraged to review the EPI. Assessment. There was no significant difference (P,0.05) between student performance on examination 3, which covered embedded information, and student performance on examination 1 which did not. Employing the Likert scale, a cumulative average of 75% and 87% of the campus and distance students rated the impact of EPI slightly positive to positive, respectively. Conclusion. Although student performance did not improve with the introduction of EPI, both campus and distance students viewed the EPI positively
Cyclotron motion in graphene
We investigate cyclotron motion in graphene monolayers considering both the
full quantum dynamics and its semiclassical limit reached at high carrier
energies. Effects of zitterbewegung due to the two dispersion branches of the
spectrum dominate the irregular quantum motion at low energies and are obtained
as a systematic correction to the semiclassical case. Recent experiments are
shown to operate in the semiclassical regime.Comment: 6 pages, 1 figure include
Quantum Hall Effects in Graphene-Based Two-Dimensional Electron Systems
In this article we review the quantum Hall physics of graphene based
two-dimensional electron systems, with a special focus on recent experimental
and theoretical developments. We explain why graphene and bilayer graphene can
be viewed respectively as J=1 and J=2 chiral two-dimensional electron gases
(C2DEGs), and why this property frames their quantum Hall physics. The current
status of experimental and theoretical work on the role of electron-electron
interactions is reviewed at length with an emphasis on unresolved issues in the
field, including assessing the role of disorder in current experimental
results. Special attention is given to the interesting low magnetic field limit
and to the relationship between quantum Hall effects and the spontaneous
anomalous Hall effects that might occur in bilayer graphene systems in the
absence of a magnetic field
The lower mass function of the young open cluster Blanco 1: from 30 Mjup to 3 Mo
We performed a deep wide field optical survey of the young (~100-150 Myr)
open cluster Blanco1 to study its low mass population well down into the brown
dwarf regime and estimate its mass function over the whole cluster mass
range.The survey covers 2.3 square degrees in the I and z-bands down to I ~ z ~
24 with the CFH12K camera. Considering two different cluster ages (100 and 150
Myr), we selected cluster member candidates on the basis of their location in
the (I,I-z) CMD relative to the isochrones, and estimated the contamination by
foreground late-type field dwarfs using statistical arguments, infrared
photometry and low-resolution optical spectroscopy. We find that our survey
should contain about 57% of the cluster members in the 0.03-0.6 Mo mass range,
including 30-40 brown dwarfs. The candidate's radial distribution presents
evidence that mass segregation has already occured in the cluster. We took it
into account to estimate the cluster mass function across the
stellar/substellar boundary. We find that, between 0.03Mo and 0.6Mo, the
cluster mass distribution does not depend much on its exact age, and is well
represented by a single power-law, with an index alpha=0.69 +/- 0.15. Over the
whole mass domain, from 0.03Mo to 3Mo, the mass function is better fitted by a
log-normal function with m0=0.36 +/- 0.07Mo and sigma=0.58 +/- 0.06. Comparison
between the Blanco1 mass function, other young open clusters' MF, and the
galactic disc MF suggests that the IMF, from the substellar domain to the
higher mass part, does not depend much on initial conditions. We discuss the
implications of this result on theories developed to date to explain the origin
of the mass distribution.Comment: 18 pages, 15 figures and 5 tables accepted in A&
Cyclotron resonance in bilayer graphene
We present the first measurements of cyclotron resonance of electrons and
holes in bilayer graphene. In magnetic fields up to B = 18 T we observe four
distinct intraband transitions in both the conduction and valence bands. The
transition energies are roughly linear in B between the lowest Landau levels,
whereas they follow \sqrt{B} for the higher transitions. This highly unusual
behavior represents a change from a parabolic to a linear energy dispersion.
The density of states derived from our data generally agrees with the existing
lowest order tight binding calculation for bilayer graphene. However in
comparing data to theory, a single set of fitting parameters fails to describe
the experimental results.Comment: to appear in Phys. Rev. Lett. Updated version with two added
references and minor text editin
On the kinematics of a corotating relativistic plasma stream in the perpendicular rotator model of a pulsar magnetosphere
An investigation of the kinematics of a rotating relativistic plasma stream
in the perpendicular rotator model of the pulsar magnetosphere is presented. It
is assumed that the plasma (ejected from the pulsar) moves along the pulsar
magnetic field lines and also corotates with them. The field lines are
considered to be radial straight lines, located in the plane which is
perpendicular to the pulsar rotation axis. The necessity of taking particle
inertia into account is discussed. It is argued that the "massless"
("force-free") approximation cannot be used for the description of this
problem. The frame selection is discussed and it is shown that it is convenient
to discuss the problem in the noninertial frame of ZAMOs (Zero Angular Momentum
Observers). The equation of motion and the exact set of equations describing
the behaviour of a relativistic plasma stream in the pulsar magnetosphere is
obtained. The possible relevance of this investigation for the understanding of
the formation process of a pulsar magnetosphere is discussed.Comment: Plain LaTe
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