9,714 research outputs found
Thermopower as a Possible Probe of Non-Abelian Quasiparticle Statistics in Fractional Quantum Hall Liquids
We show in this paper that thermopower is enhanced in non-Abelian quantum
Hall liquids under appropriate conditions. This is because thermopower measures
entropy per electron in the clean limit, while the degeneracy and entropy
associated with non-Abelian quasiparticles enhance entropy when they are
present. Thus thermopower can potentially probe non-Abelian nature of the
quasiparticles, and measure their quantum dimension.Comment: 5 pages. Minor revisions in response to referee comments. Published
versio
Theory of the Nernst effect near quantum phase transitions in condensed matter, and in dyonic black holes
We present a general hydrodynamic theory of transport in the vicinity of
superfluid-insulator transitions in two spatial dimensions described by
"Lorentz"-invariant quantum critical points. We allow for a weak impurity
scattering rate, a magnetic field B, and a deviation in the density, \rho, from
that of the insulator. We show that the frequency-dependent thermal and
electric linear response functions, including the Nernst coefficient, are fully
determined by a single transport coefficient (a universal electrical
conductivity), the impurity scattering rate, and a few thermodynamic state
variables. With reasonable estimates for the parameters, our results predict a
magnetic field and temperature dependence of the Nernst signal which resembles
measurements in the cuprates, including the overall magnitude. Our theory
predicts a "hydrodynamic cyclotron mode" which could be observable in ultrapure
samples. We also present exact results for the zero frequency transport
co-efficients of a supersymmetric conformal field theory (CFT), which is
solvable by the AdS/CFT correspondence. This correspondence maps the \rho and B
perturbations of the 2+1 dimensional CFT to electric and magnetic charges of a
black hole in the 3+1 dimensional anti-de Sitter space. These exact results are
found to be in full agreement with the general predictions of our hydrodynamic
analysis in the appropriate limiting regime. The mapping of the hydrodynamic
and AdS/CFT results under particle-vortex duality is also described.Comment: 44 pages, 4 figures; (v3) Added new subsection highlighting negative
Hall resistance at hole densities smaller than 1/
An electromagnetic shashlik calorimeter with longitudinal segmentation
A novel technique for longitudinal segmentation of shashlik calorimeters has
been tested in the CERN West Area beam facility. A 25 tower very fine samplings
e.m. calorimeter has been built with vacuum photodiodes inserted in the first 8
radiation lengths to sample the initial development of the shower. Results
concerning energy resolution, impact point reconstruction and electron/pion
separation are reported.Comment: 13 pages, 12 figure
Quasiparticle Hall Transport of d-wave Superconductors in Vortex State
We present a theory of quasiparticle Hall transport in strongly type-II
superconductors within their vortex state. We establish the existence of
integer quantum spin Hall effect in clean unconventional
superconductors in the vortex state from a general analysis of the
Bogoliubov-de Gennes equation. The spin Hall conductivity is
shown to be quantized in units of . This result does not
rest on linearization of the BdG equations around Dirac nodes and therefore
includes inter-nodal physics in its entirety. In addition, this result holds
for a generic inversion-symmetric lattice of vortices as long as the magnetic
field satisfies . We then derive the
Wiedemann-Franz law for the spin and thermal Hall conductivity in the vortex
state. In the limit of , the thermal Hall conductivity satisfies
. The
transitions between different quantized values of as well as
relation to conventional superconductors are discussed.Comment: 18 pages REVTex, 3 figures, references adde
Thermohydrodynamics in Quantum Hall Systems
A theory of thermohydrodynamics in two-dimensional electron systems in
quantizing magnetic fields is developed including a nonlinear transport regime.
Spatio-temporal variations of the electron temperature and the chemical
potential in the local equilibrium are described by the equations of
conservation with the number and thermal-energy flux densities. A model of
these flux densities due to hopping and drift processes is introduced for a
random potential varying slowly compared to both the magnetic length and the
phase coherence length. The flux measured in the standard transport experiment
is derived and is used to define a transport component of the flux density. The
equations of conservation can be written in terms of the transport component
only. As an illustration, the theory is applied to the Ettingshausen effect, in
which a one-dimensional spatial variation of the electron temperature is
produced perpendicular to the current.Comment: 10 pages, 1 figur
Laser-induced etching of few-layer graphene synthesized by Rapid-Chemical Vapour Deposition on Cu thin films
The outstanding electrical and mechanical properties of graphene make it very
attractive for several applications, Nanoelectronics above all. However a
reproducible and non destructive way to produce high quality, large-scale area,
single layer graphene sheets is still lacking. Chemical Vapour Deposition of
graphene on Cu catalytic thin films represents a promising method to reach this
goal, because of the low temperatures (T < 900 Celsius degrees) involved during
the process and of the theoretically expected monolayer self-limiting growth.
On the contrary such self-limiting growth is not commonly observed in
experiments, thus making the development of techniques allowing for a better
control of graphene growth highly desirable. Here we report about the local
ablation effect, arising in Raman analysis, due to the heat transfer induced by
the laser incident beam onto the graphene sample.Comment: v1:9 pages, 8 figures, submitted to SpringerPlus; v2: 11 pages,
PDFLaTeX, 9 figures, revised peer-reviewed version resubmitted to
SpringerPlus; 1 figure added, figure 1 and 4 replaced,typos corrected,
"Results and discussion" section significantly extended to better explain
etching mechanism and features of Raman spectra, references adde
Top-Charm Associated Production in High Energy Collisions
The possibility of exploring the flavor changing neutral current
couplings in the production vertex for the reaction \epem\to
t\bar c + \bar tc is examined. Using a model independent parameterization for
the effective Lagrangian to describe the most general three-point interactions,
production cross sections are found to be relatively small at LEP II, but
potentially sizeable at higher energy \epem colliders. The kinematic
characteristics of the signal are studied and a set of cuts are devised for
clean separation of the signal from background. The resulting sensitivity to
anomalous flavor changing couplings at LEP II with an integrated luminosity of
pb is found to be comparable to their present indirect
constraints from loop processes, while at higher energy colliders with
TeV center-of-mass energy and 50-200 fb luminosity, one expects to reach
a sensitivity at or below the percentage level.Comment: Latex, 22 page
Effective electro-optical modulation with high extinction ratio by a graphene-silicon microring resonator
Graphene opens up for novel optoelectronic applications thanks to its high
carrier mobility, ultra-large absorption bandwidth, and extremely fast material
response. In particular, the opportunity to control optoelectronic properties
through tuning of Fermi level enables electro-optical modulation,
optical-optical switching, and other optoelectronics applications. However,
achieving a high modulation depth remains a challenge because of the modest
graphene-light interaction in the graphene-silicon devices, typically,
utilizing only a monolayer or few layers of graphene. Here, we comprehensively
study the interaction between graphene and a microring resonator, and its
influence on the optical modulation depth. We demonstrate graphene-silicon
microring devices showing a high modulation depth of 12.5 dB with a relatively
low bias voltage of 8.8 V. On-off electro-optical switching with an extinction
ratio of 3.8 dB is successfully demonstrated by applying a square-waveform with
a 4 V peak-to-peak voltage.Comment: 12 pages, including 7 figure
Thermoelectric Response of an Interacting Two-Dimensional Electron Gas in Quantizing Magnetic Field
We present a discussion of the linear thermoelectric response of an
interacting electron gas in a quantizing magnetic field. Boundary currents can
carry a significant fraction of the net current passing through the system. We
derive general expressions for the bulk and boundary components of the number
and energy currents. We show that the local current density may be described in
terms of ``transport'' and ``internal magnetization'' contributions. The latter
carry no net current and are not observable in standard transport experiments.
We show that although Onsager relations cannot be applied to the local current,
they are valid for the transport currents and hence for the currents observed
in standard transport experiments. We relate three of the four thermoelectric
response coefficients of a disorder-free interacting two-dimensional electron
gas to equilibrium thermodynamic quantities. In particular, we show that the
diffusion thermopower is proportional to the entropy per particle, and we
compare this result with recent experimental observations.Comment: 18 pages, 2 postscript figures included. Revtex with epsf.tex and
multicol.sty. In the revised version, the comparison with experimental
observations at is extended to include the possibility of
corrections due to weak impurity scattering. The conclusions that we reach
regarding the applicability of the composite fermion model at these filling
fractions are not affecte
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