4,781 research outputs found
Vanishing Hall Resistance at High Magnetic Field in a Double Layer Two-Dimensional Electron System
At total Landau level filling factor a double layer
two-dimensional electron system with small interlayer separation supports a
collective state possessing spontaneous interlayer phase coherence. This state
exhibits the quantized Hall effect when equal electrical currents flow in
parallel through the two layers. In contrast, if the currents in the two layers
are equal, but oppositely directed, both the longitudinal and Hall resistances
of each layer vanish in the low temperature limit. This finding supports the
prediction that the ground state at is an excitonic superfluid.Comment: 4 pages, 4 figure
Evidence for a fractional quantum Hall state with anisotropic longitudinal transport
At high magnetic fields, where the Fermi level lies in the N=0 lowest Landau
level (LL), a clean two-dimensional electron system (2DES) exhibits numerous
incompressible liquid phases which display the fractional quantized Hall effect
(FQHE) (Das Sarma and Pinczuk, 1997). These liquid phases do not break
rotational symmetry, exhibiting resistivities which are isotropic in the plane.
In contrast, at lower fields, when the Fermi level lies in the third
and several higher LLs, the 2DES displays a distinctly different class of
collective states. In particular, near half filling of these high LLs the 2DES
exhibits a strongly anisotropic longitudinal resistance at low temperatures
(Lilly et al., 1999; Du et al., 1999). These "stripe" phases, which do not
exhibit the quantized Hall effect, resemble nematic liquid crystals, possessing
broken rotational symmetry and orientational order (Koulakov et al., 1996;
Fogler et al., 1996; Moessner and Chalker, 1996; Fradkin and Kivelson, 1999;
Fradkin et al, 2010). Here we report a surprising new observation: An
electronic configuration in the N=1 second LL whose resistivity tensor
simultaneously displays a robust fractionally quantized Hall plateau and a
strongly anisotropic longitudinal resistance resembling that of the stripe
phases.Comment: Nature Physics, (2011
Noisy regression and classification with continuous multilayer networks
We investigate zero temperature Gibbs learning for two classes of
unrealizable rules which play an important role in practical applications of
multilayer neural networks with differentiable activation functions:
classification problems and noisy regression problems. Considering one step of
replica symmetry breaking, we surprisingly find that for sufficiently large
training sets the stable state is replica symmetric even though the target rule
is unrealizable. Further, the classification problem is shown to be formally
equivalent to the noisy regression problem.Comment: 7 pages, including 2 figure
Coulomb Drag in the Extreme Quantum Limit
Coulomb drag resulting from interlayer electron-electron scattering in double
layer 2D electron systems at high magnetic field has been measured. Within the
lowest Landau level the observed drag resistance exceeds its zero magnetic
value by factors of typically 1000. At half-filling of the lowest Landau level
in each layer (nu = 1/2) the data suggest that our bilayer systems are much
more strongly correlated than recent theoretical models based on perturbatively
coupled composite fermion metals.Comment: 4 pages, 4 figure
Transition from quantum Hall to compressible states in the second Landau level: new light on the =5/2 enigma
Quantum Hall states at filling fraction =5/2 are examined by numerical
diagonalization. Spin-polarized and -unpolarized states of systems with electrons are studied, neglecting effects of Landau level mixing. We find
that the ground state is spin polarized. It is incompressible and has a large
overlap with paired states like the Pfaffian. For a given sample, the energy
gap is about 11 times smaller than at =1/3. Evidence is presented of phase
transitions to compressible states, driven by the interaction strength at short
distance. A reinterpretation of experiments is suggested.Comment: This paper has already appeared in PRL, but has not been on the we
Learning and predicting time series by neural networks
Artificial neural networks which are trained on a time series are supposed to
achieve two abilities: firstly to predict the series many time steps ahead and
secondly to learn the rule which has produced the series. It is shown that
prediction and learning are not necessarily related to each other. Chaotic
sequences can be learned but not predicted while quasiperiodic sequences can be
well predicted but not learned.Comment: 5 page
Observation of narrow-band noise accompanying the breakdown of insulating states in high Landau levels
Recent magnetotransport experiments on high mobility two-dimensional electron
systems have revealed many-body electron states unique to high Landau levels.
Among these are re-entrant integer quantum Hall states which undergo sharp
transitions to conduction above some threshold field. Here we report that these
transitions are often accompanied by narrow- and broad-band noise with
frequencies which are strongly dependent on the magnitude of the applied dc
current.Comment: 4 pages, 3 figure
Clustering of Photometric Luminous Red Galaxies II: Cosmological Implications from the Baryon Acoustic Scale
A new determination of the sound horizon scale in angular coordinates is
presented. It makes use of ~ 0.6 x 10^6 Luminous Red Galaxies, selected from
the Sloan Digital Sky Survey imaging data, with photometric redshifts. The
analysis covers a redshift interval that goes from z=0.5 to z=0.6. We find
evidence of the Baryon Acoustic Oscillations (BAO) signal at the ~ 2.3 sigma
confidence level, with a value of theta_{BAO} (z=0.55) = (3.90 \pm 0.38)
degrees, including systematic errors. To our understanding, this is the first
direct measurement of the angular BAO scale in the galaxy distribution, and it
is in agreement with previous BAO measurements. We also show how radial
determinations of the BAO scale can break the degeneracy in the measurement of
cosmological parameters when they are combined with BAO angular measurements.
The result is also in good agreement with the WMAP7 best-fit cosmology. We
obtain a value of w_0 = -1.03 \pm 0.16 for the equation of state parameter of
the dark energy, Omega_M = 0.26 \pm 0.04 for the matter density, when the other
parameters are fixed. We have also tested the sensitivity of current BAO
measurements to a time varying dark energy equation of state, finding w_a =
0.06 \pm 0.22 if we fix all the other parameters to the WMAP7 best-fit
cosmology.Comment: 7 pages, 7 figures, Accepted for publication to MNRA
Insulating and Fractional Quantum Hall States in the N=1 Landau Level
The observation of new insulating phases of two-dimensional electrons in the
first excited Landau level is reported. These states, which are manifested as
re-entrant integer quantized Hall effects, exist alongside well-developed
even-denominator fractional quantized Hall states at nu=7/2 and 5/2 and new
odd-denominator states at nu=3+1/5 and 3+4/5.Comment: 4 pages, 3 figure
Competition and Selection Among Conventions
In many domains, a latent competition among different conventions determines
which one will come to dominate. One sees such effects in the success of
community jargon, of competing frames in political rhetoric, or of terminology
in technical contexts. These effects have become widespread in the online
domain, where the data offers the potential to study competition among
conventions at a fine-grained level.
In analyzing the dynamics of conventions over time, however, even with
detailed on-line data, one encounters two significant challenges. First, as
conventions evolve, the underlying substance of their meaning tends to change
as well; and such substantive changes confound investigations of social
effects. Second, the selection of a convention takes place through the complex
interactions of individuals within a community, and contention between the
users of competing conventions plays a key role in the convention's evolution.
Any analysis must take place in the presence of these two issues.
In this work we study a setting in which we can cleanly track the competition
among conventions. Our analysis is based on the spread of low-level authoring
conventions in the eprint arXiv over 24 years: by tracking the spread of macros
and other author-defined conventions, we are able to study conventions that
vary even as the underlying meaning remains constant. We find that the
interaction among co-authors over time plays a crucial role in the selection of
them; the distinction between more and less experienced members of the
community, and the distinction between conventions with visible versus
invisible effects, are both central to the underlying processes. Through our
analysis we make predictions at the population level about the ultimate success
of different synonymous conventions over time--and at the individual level
about the outcome of "fights" between people over convention choices.Comment: To appear in Proceedings of WWW 2017, data at
https://github.com/CornellNLP/Macro
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