9,161 research outputs found
Interference, Coulomb blockade, and the identification of non-abelian quantum Hall states
We examine the relation between different electronic transport phenomena in a
Fabry-Perot interferometer in the fractional quantum Hall regime. In
particular, we study the way these phenomena reflect the statistics of quantum
Hall quasi-particles. For two series of states we examine, one abelian and one
non-abelian, we show that the information that may be obtained from
measurements of the lowest order interference pattern in an open Fabry-Perot
interferometer is identical to the one that may be obtained from the
temperature dependence of Coulomb blockade peaks in a closed interferometer. We
argue that despite the similarity between the experimental signatures of the
two series of states, interference and Coulomb blockade measurements are likely
to be able to distinguish between abelian and non-abelian states, due to the
sensitivity of the abelian states to local perturbations, to which the
non-abelian states are insensitive.Comment: 10 pages. Published versio
Bulk-edge coupling in the non-abelian quantum Hall interferometer
Recent schemes for experimentally probing non-abelian statistics in the
quantum Hall effect are based on geometries where current-carrying
quasiparticles flow along edges that encircle bulk quasiparticles, which are
localized. Here we consider one such scheme, the Fabry-Perot interferometer,
and analyze how its interference patterns are affected by a coupling that
allows tunneling of neutral Majorana fermions between the bulk and edge. While
at weak coupling this tunneling degrades the interference signal, we find that
at strong coupling, the bulk quasiparticle becomes essentially absorbed by the
edge and the intereference signal is fully restored.Comment: 5 pages, 1 figur
Composite Fermions with Orbital Magnetization
For quantum Hall systems, in the limit of large magnetic field (or
equivalently small electron band mass ), the static response of electrons
to a spatially varying magnetic field is largely determined by kinetic energy
considerations. This response is not correctly given in existing approximations
based on the Fermion Chern-Simons theory of the partially filled Landau level.
We remedy this problem by attaching an orbital magnetization to each fermion to
separate the current into magnetization and transport contributions, associated
with the cyclotron and guiding center motions respectively. This leads to a
Chern-Simons Fermi liquid description of the state which
correctly predicts the dependence of the static and dynamic response in
the limit .Comment: 4 pages, RevTeX, no figure
Properties of Quantum Hall Skyrmions from Anomalies
It is well known that the Fractional Quantum Hall Effect (FQHE) may be
effectively represented by a Chern-Simons theory. In order to incorporate QH
Skyrmions, we couple this theory to the topological spin current, and include
the Hopf term. The cancellation of anomalies for chiral edge states, and the
proviso that Skyrmions may be created and destroyed at the edge, fixes the
coefficients of these new terms. Consequently, the charge and the spin of the
Skyrmion are uniquely determined. For those two quantities we find the values
and , respectively, where is electron charge,
is the filling fraction and is the Skyrmion winding number. We
also add terms to the action so that the classical spin fluctuations in the
bulk satisfy the standard equations of a ferromagnet, with spin waves that
propagate with the classical drift velocity of the electron.Comment: 8 pages, LaTeX file; Some remarks are included to clarify the
physical results obtained, and the role of the Landau-Lifshitz equation is
emphasized. Some references adde
Which Way Was I Going? Contextual Retrieval Supports the Disambiguation of Well Learned Overlapping Navigational Routes
Groundbreaking research in animals has demonstrated that the hippocampus contains neurons that distinguish betweenoverlapping navigational trajectories. These hippocampal neurons respond selectively to the context of specific episodes despite interference from overlapping memory representations. The present study used functional magnetic resonanceimaging in humans to examine the role of the hippocampus and related structures when participants need to retrievecontextual information to navigate well learned spatial sequences that share common elements. Participants were trained outside the scanner to navigate through 12 virtual mazes from a ground-level first-person perspective. Six of the 12 mazes shared overlapping components. Overlapping mazes began and ended at distinct locations, but converged in the middle to share some hallways with another maze. Non-overlapping mazes did not share any hallways with any other maze. Successful navigation through the overlapping hallways required the retrieval of contextual information relevant to thecurrent navigational episode. Results revealed greater activation during the successful navigation of the overlapping mazes compared with the non-overlapping mazes in regions typically associated with spatial and episodic memory, including thehippocampus, parahippocampal cortex, and orbitofrontal cortex. When combined with previous research, the current findings suggest that an anatomically integrated system including the hippocampus, parahippocampal cortex, and orbitofrontal cortexis critical for the contextually dependent retrieval of well learned overlapping navigational routes
NICMOS Imaging of the Dusty Microjansky Radio Source VLA J123642+621331 at z = 4.424
We present the discovery of a radio galaxy at a likely redshift of z = 4.424
in one of the flanking fields of the Hubble Deep Field. Radio observations with
the VLA and MERLIN centered on the HDF yielded a complete sample of microjansky
radio sources, of which about 20% have no optical counterpart to I < 25 mag. In
this Letter, we address the possible nature of one of these sources, through
deep HST NICMOS images in the F110W (J) and F160W (H) filters. VLA
J123642+621331 has a single emission line at 6595-A, which we identify with
Lyman-alpha at z = 4.424. We argue that this faint (H = 23.9 mag), compact (r =
0.2 arcsec), red (I - K = 2.0) object is most likely a dusty, star-forming
galaxy with an embedded active nucleus.Comment: Accepted for publication in Astrophysical Journal Letters. 11 pages,
4 figures, uses aastex v5.0 and psfi
Strong enhancement of drag and dissipation at the weak- to strong- coupling phase transition in a bi-layer system at a total Landau level filling nu=1
We consider a bi-layer electronic system at a total Landau level filling
factor nu =1, and focus on the transition from the regime of weak inter-layer
coupling to that of the strongly coupled (1,1,1) phase (or ''quantum Hall
ferromagnet''). Making the assumption that in the transition region the system
is made of puddles of the (1,1,1) phase embedded in a bulk of the weakly
coupled state, we show that the transition is accompanied by a strong increase
in longitudinal Coulomb drag, that reaches a maximum of approximately
. In that regime the longitudinal drag is increased with decreasing
temperature.Comment: four pages, one included figur
Composite Fermions in Modulated Structures: Transport and Surface Acoustic Waves
Motivated by a recent experiment of Willett et al. [Phys. Rev. Lett. 78, 4478
(1997)], we employ semiclassical composite-fermion theory to study the effect
of a periodic density modulation on a quantum Hall system near Landau level
filling factor nu=1/2. We show that even a weak density modulation leads to
dramatic changes in surface-acoustic-wave (SAW) propagation, and propose an
explanation for several key features of the experimental observations. We
predict that properly arranged dc transport measurements would show a structure
similar to that seen in SAW measurements.Comment: Version published in Phys. Rev. Lett. Figures changed to show SAW
velocity shift. LaTeX, 5 pages, two included postscript figure
- …