5,236 research outputs found
Observation of chiral heat transport in the quantum Hall regime
Heat transport in the quantum Hall regime is investigated using micron-scale heaters and thermometers positioned along the edge of a millimeter-scale two dimensional electron system (2DES). The heaters rely on localized current injection into the 2DES, while the thermometers are based on the thermoelectric effect. In the v=1 integer quantized Hall state, a thermoelectric signal appears at an edge thermometer only when it is “downstream,” in the sense of electronic edge transport, from the heater. When the distance between the heater and the thermometer is increased, the thermoelectric signal is reduced, showing that the electrons cool as they propagate along the edge
Evidence for a Goldstone Mode in a Double Layer Quantum Hall System
The tunneling conductance between two parallel 2D electron systems has been
measured in a regime of strong interlayer Coulomb correlations. At total Landau
level filling the tunnel spectrum changes qualitatively when the
boundary separating the compressible phase from the ferromagnetic quantized
Hall state is crossed. A huge resonant enhancement replaces the strongly
suppressed equilibrium tunneling characteristic of weakly coupled layers. The
possible relationship of this enhancement to the Goldstone mode of the broken
symmetry ground state is discussed.Comment: 4 pages, 3 figures, 2 minor typeos fixe
Tunneling Conductance Between Parallel Two Dimensional Electron Systems
We derive and evaluate expressions for the low temperature {\it dc}
equilibrium tunneling conductance between parallel two-dimensional electron
systems. Our theory is based on a linear-response formalism and on
impurity-averaged perturbation theory. The disorder broadening of features in
the dependence of tunneling conductance on sheet densities and in-plane
magnetic field strengths is influenced both by the finite lifetime of electrons
within the wells and by non-momentum-conserving tunneling events. Disorder
vertex corrections are important only for weak in-plane magnetic fields and
strong interwell impurity-potential correlations. We comment on the basis of
our results on the possibility of using tunneling measurements to determine the
lifetime of electrons in the quantum wells.Comment: 14 pages, 5 Fig. not included, revtex, IUcm92-00
The scale-dependence of relative galaxy bias: encouragement for the halo model description
We investigate the relationship between the colors, luminosities, and
environments of galaxies in the Sloan Digital Sky Survey spectroscopic sample,
using environmental measurements on scales ranging from 0.2 to 6 Mpc/h. We
find: (1) that the relationship between color and environment persists even to
the lowest luminosities we probe (absolute magnitude in the r band of about -14
for h=1); (2) at luminosities and colors for which the galaxy correlation
function has a large amplitude, it also has a steep slope; and (3) in regions
of a given overdensity on small scales (1 Mpc/h), the overdensity on large
scales (6 Mpc/h) does not appear to relate to the recent star formation history
of the galaxies. Of these results, the last has the most immediate application
to galaxy formation theory. In particular, it lends support to the notion that
a galaxy's properties are related only to the mass of its host dark matter
halo, and not to the larger scale environment.Comment: submitted to ApJ; full resolution figures and slide material
available at http://cosmo.nyu.edu/blanton/scale_density.htm
Improved cosmological constraints on the curvature and equation of state of dark energy
We apply the Constitution compilation of 397 supernova Ia, the baryon
acoustic oscillation measurements including the parameter, the distance
ratio and the radial data, the five-year Wilkinson microwave anisotropy probe
and the Hubble parameter data to study the geometry of the universe and the
property of dark energy by using the popular Chevallier-Polarski-Linder and
Jassal-Bagla-Padmanabhan parameterizations. We compare the simple
method of joined contour estimation and the Monte Carlo Markov chain method,
and find that it is necessary to make the marginalized analysis on the error
estimation. The probabilities of and in the
Chevallier-Polarski-Linder model are skew distributions, and the marginalized
errors are ,
, , and
. For the Jassal-Bagla-Padmanabhan model, the
marginalized errors are ,
, , and
. The equation of state parameter of dark energy
is negative in the redshift range at more than level.
The flat CDM model is consistent with the current observational data
at the level.Comment: 10 figures, 12 pages, Classical and Quantum Gravity in press; v2 to
match the pulished versio
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
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
Dark energy and curvature from a future baryonic acoustic oscillation survey using the Lyman-alpha forest
We explore the requirements for a Lyman-alpha forest (LyaF) survey designed
to measure the angular diameter distance and Hubble parameter at 2~<z~<4 using
the standard ruler provided by baryonic acoustic oscillations (BAO). The goal
would be to obtain a high enough density of sources to probe the
three-dimensional density field on the scale of the BAO feature. A
percent-level measurement in this redshift range can almost double the Dark
Energy Task Force Figure of Merit, relative to the case with only a similar
precision measurement at z~1, if the Universe is not assumed to be flat. This
improvement is greater than the one obtained by doubling the size of the z~1
survey, with Planck and a weak SDSS-like z=0.3 BAO measurement assumed in each
case. Galaxy BAO surveys at z~1 may be able to make an effective LyaF
measurement simultaneously at minimal added cost, because the required number
density of quasars is relatively small. We discuss the constraining power as a
function of area, magnitude limit (density of quasars), resolution, and
signal-to-noise of the spectra. For example, a survey covering 2000 sq. deg.
and achieving S/N=1.8 per Ang. at g=23 (~40 quasars per sq. deg.) with an
R~>250 spectrograph is sufficient to measure both the radial and transverse
oscillation scales to 1.4% from the LyaF (or better, if fainter magnitudes and
possibly Lyman-break galaxies can be used). At fixed integration time and in
the sky-noise-dominated limit, a wider, noisier survey is generally more
efficient; the only fundamental upper limit on noise being the need to identify
a quasar and find a redshift. Because the LyaF is much closer to linear and
generally better understood than galaxies, systematic errors are even less
likely to be a problem.Comment: 18 pages including 6 figures, submitted to PR
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