1,186 research outputs found
Peripheral Fluorescein Angiographic Findings in Fellow Eyes of Patients with Branch Retinal Vein Occlusion
Introduction. Branch retinal vein occlusion (BRVO) is a common retinal vascular condition that results in intraocular inflammatory changes. Ultra wide field fluorescein angiography (UWFFA) is a retinal imaging device that can capture peripheral retinal findings. The purpose of this study was to look for peripheral findings in the fellow eye of patients with BRVO using UWFFA. Methods. Retrospective imaging review of patients diagnosed with BRVO that had both eyes imaged with UWFFA. Images were graded for peripheral findings in other quadrants of the same eye as well as in all quadrants of the fellow eye. Results. Of 81 patients, 14 (17%) patients had late vascular leakage in a quadrant other than the BRVO distribution. Five (6%) findings were in the same eye, 8 (10%) findings were in the fellow eye, and 1 (1%) finding was in both the same eye and the fellow eye. Of these 14 patients, 11 (80%) patients had hypertension. Conclusion. Late peripheral retinal leakage in the fellow eye of patients with BRVO was detected in this cohort of patients with UWFFA. This novel finding may represent underlying systemic inflammation, hypertension, or bilateral BRVOs
Transverse optical plasmons in layered superconductors
We discuss the possible existance of transverse optical plasma modes in
superlattices consisting of Josephson coupled superconducting layers. These
modes appear as resonances in the current-current correlation function, as
opposed to the usual plasmons which are poles in the density-density channel.
We consider both bilayer superlattices, and single layer lattices with a spread
of interlayer Josephson couplings. We show that our model is in quantitative
agreement with the recent experimental observation by a number of groups of a
peak at the Josephson plasma frequency in the optical conductivity of
LaSrCuOComment: Proceedings of LT21, in press, 4 pages, Latex with LTpaper.sty and
epsfig.sty, 2 postscript figure
Multicomponent fractional quantum Hall effect in graphene
We report observation of the fractional quantum Hall effect (FQHE) in high
mobility multi-terminal graphene devices, fabricated on a single crystal boron
nitride substrate. We observe an unexpected hierarchy in the emergent FQHE
states that may be explained by strongly interacting composite Fermions with
full SU(4) symmetric underlying degrees of freedom. The FQHE gaps are measured
from temperature dependent transport to be up 10 times larger than in any other
semiconductor system. The remarkable strength and unusual hierarcy of the FQHE
described here provides a unique opportunity to probe correlated behavior in
the presence of expanded quantum degrees of freedom.Comment: 5 pages, 3 figure
Experimental Test of the Inter-Layer Pairing Models for High-Tc Superconductivity Using Grazing Incidence Infrared Reflectometry
From measurements of the far-infrared reflectivity at grazing angles of
incidence with p-polarized light we determined the c-axis Josephson plasma
frequencies of the single layer high T_c cuprates Tl_2Ba_2CuO_6 and
La_{2-x}Sr_xCuO_4. We detected a strong plasma resonance at 50 cm^{-1} for
La_{2-x}Sr_xCuO_4 in excellent agreement with previously published results. For
Tl_2Ba_2CuO_6 we were able to determine an upper limit of the unscreened c-axis
Josephson plasma frequency 100 cm^{-1} or a c-axis penetration depth > 15 \mu
m. The small value of stands in contrast to recent a prediction
based on the inter-layer tunneling mechanism of superconductivity.Comment: 4 pages, Phys. Rev. B, in press, Revtex, 4 postscript figure
Observation of the Fractional Quantum Hall Effect in Graphene
When electrons are confined in two dimensions and subjected to strong
magnetic fields, the Coulomb interactions between them become dominant and can
lead to novel states of matter such as fractional quantum Hall liquids. In
these liquids electrons linked to magnetic flux quanta form complex composite
quasipartices, which are manifested in the quantization of the Hall
conductivity as rational fractions of the conductance quantum. The recent
experimental discovery of an anomalous integer quantum Hall effect in graphene
has opened up a new avenue in the study of correlated 2D electronic systems, in
which the interacting electron wavefunctions are those of massless chiral
fermions. However, due to the prevailing disorder, graphene has thus far
exhibited only weak signatures of correlated electron phenomena, despite
concerted experimental efforts and intense theoretical interest. Here, we
report the observation of the fractional quantum Hall effect in ultraclean
suspended graphene, supporting the existence of strongly correlated electron
states in the presence of a magnetic field. In addition, at low carrier density
graphene becomes an insulator with an energy gap tunable by magnetic field.
These newly discovered quantum states offer the opportunity to study a new
state of matter of strongly correlated Dirac fermions in the presence of large
magnetic fields
Melting of a 2D Quantum Electron Solid in High Magnetic Field
The melting temperature () of a solid is generally determined by the
pressure applied to it, or indirectly by its density () through the equation
of state. This remains true even for helium solids\cite{wilk:67}, where quantum
effects often lead to unusual properties\cite{ekim:04}. In this letter we
present experimental evidence to show that for a two dimensional (2D) solid
formed by electrons in a semiconductor sample under a strong perpendicular
magnetic field\cite{shay:97} (), the is not controlled by , but
effectively by the \textit{quantum correlation} between the electrons through
the Landau level filling factor =. Such melting behavior, different
from that of all other known solids (including a classical 2D electron solid at
zero magnetic field\cite{grim:79}), attests to the quantum nature of the
magnetic field induced electron solid. Moreover, we found the to increase
with the strength of the sample-dependent disorder that pins the electron
solid.Comment: Some typos corrected and 2 references added. Final version with minor
editoriol revisions published in Nature Physic
Effective Mass of Composite Fermions and Fermionic Chern-Simons Theory in Temporal Gauge
The definitions of the effective mass of the composite fermion are discussed
for the half-filled Landau level problem. In a recent work, Shankar and Murthy
show a finite effective mass of the composite fermion by a canonical
transformation while the perturbative calculation gives the logarithmic
divergence of the effective mass at the Fermi surface. We will emphasize that
the different definition of the effective mass has the different physical
processes. The finite one could be defined for any momentum of the composite
fermion while the divergence only appears at the Fermi surface. We work with
the standard Halperin-Lee-Read model but in the temporal gauge. The advantage
of this gauge to be employed is that the finite effective mass could be
calculated in the Hartree-Fock approximation. Furthermore, it is precisely
equal to the result that Shankar and Murthy obtained which is well-fit with the
numerical calculation from the ground state energy analysis and a
semi-classical estimation. However, if we consider the random phase
approximation, one sees that the divergence of the effective mass of the
quasiparticle at the Fermi surface emerges again no matter that we work on the
temporal or Coulomb gauges. We develop an effective theory where the finite
effective mass serves as a `bare' effective mass and show that the same
divergence of the RPA effective mass. On the other hand, the correct behavior
of the response functions in the small band mass limit could be seen clearly in
the temporal gauge since there is a self-interaction among the magnetoplasmons.Comment: 27 pages,6 eps figure
Analysis of Shot Noise at Finite Temperatures in Fractional Quantum Hall Edge States
We investigate shot noise at {\it finite temperatures} induced by the
quasi-particle tunneling between fractional quantum Hall (FQH) edge states. The
resulting Fano factor has the peak structure at a certain bias voltage. Such a
structure indicates that quasi-particles are weakly {\it glued} due to thermal
fluctuation. We show that the effect makes it possible to probe the difference
of statistics between FQH states where quasi-particles have the
same unit charge.Finally we propose a way to indirectly obtain statistical
angle in hierarchical FQH states.Comment: 5 pages, 3 figure
Coexistence of the topological state and a two-dimensional electron gas on the surface of Bi2Se3
Topological insulators are a recently discovered class of materials with
fascinating properties: While the inside of the solid is insulating,
fundamental symmetry considerations require the surfaces to be metallic. The
metallic surface states show an unconventional spin texture, electron dynamics
and stability. Recently, surfaces with only a single Dirac cone dispersion have
received particular attention. These are predicted to play host to a number of
novel physical phenomena such as Majorana fermions, magnetic monopoles and
unconventional superconductivity. Such effects will mostly occur when the
topological surface state lies in close proximity to a magnetic or electric
field, a (superconducting) metal, or if the material is in a confined geometry.
Here we show that a band bending near to the surface of the topological
insulator BiSe gives rise to the formation of a two-dimensional
electron gas (2DEG). The 2DEG, renowned from semiconductor surfaces and
interfaces where it forms the basis of the integer and fractional quantum Hall
effects, two-dimensional superconductivity, and a plethora of practical
applications, coexists with the topological surface state in BiSe. This
leads to the unique situation where a topological and a non-topological, easily
tunable and potentially superconducting, metallic state are confined to the
same region of space.Comment: 12 pages, 3 figure
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