2,254 research outputs found
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-driven breakdown of the 331 state and the emergent Pfaffian and composite Fermi liquid phases
We examine the possibility of creating the Moore-Read Pfaffian in the lowest
Landau level when the multicomponent Halperin 331 state (believed to describe
quantum Hall bilayers and wide quantum wells at the filling factor )
is destroyed by the increase of tunneling. Using exact diagonalization of the
bilayer Hamiltonian with short-range and long-range (Coulomb) interactions in
spherical and periodic rectangular geometries, we establish that tunneling is a
perturbation that drives the 331 state into a compressible composite Fermi
liquid, with the possibility for an intermediate critical state that possesses
some properties of the Moore-Read Pfaffian. These results are interpreted in
the two-component BCS model for Cauchy pairing with a tunneling constraint. We
comment on the conditions to be imposed on a system with fluctuating density in
order to achieve the stable Pfaffian phase.Comment: 10 pages, 7 figure
Incidence and medical management of bisphosphonate-associated atypical femoral fractures in a major trauma centre: a retrospective observational study
BACKGROUND: Atypical femoral fractures (AFFs) are rare events associated with increased duration of bisphosphonate exposure. Recommended management of AFFs include cessation of bisphosphonates and imaging of the contralateral femur. The aims of this study were to identify the local incidence of AFFs in bisphosphonate users and to audit the medical management of AFFs against published recommendations. METHODS: A retrospective analysis of the admissions database for a major trauma centre identified all femoral fractures (3150) in a five-year period (July 2009 to June 2014). Electronic health records and radiographs were reviewed using the 2013 American Society for Bone and Mineral Research (ASBMR) diagnostic criteria for AFF to establish the number of cases. To estimate incidence, the total number of bisphosphonate users was derived from primary care prescription and secondary care day-case records. Medical management of cases with AFF on bisphosphonates was audited against guidance from ASBMR and Medicines & Healthcare Products Regulatory Agency. RESULTS: 10 out of 3150 femoral fractures met criteria for AFF; 7 of these patients had a history of exposure to bisphosphonates (6 oral, 1 intravenous). There were 19.1 AFFs per 100,000Â years of bisphosphonate use in our region. Bisphosphonates were stopped and the contralateral femur imaged in only 2 of the 7 patients treated with bisphosphonates. CONCLUSION: Our local incidence is in line with published figures; however, this is the first published evidence suggesting that medical management and identification of AFF may be suboptimal. Managing these patients remains challenging due to their rarity and possible lack of awareness
Spontaneous coherence and the quantum Hall Effect in triple-layer electron systems
We investigate spontaneous interlayer phase coherence and the occurrence of
the quantum Hall effect in triple-layer electron systems. Our work is based on
a simple tight-binding model that greatly facilitates calculations and whose
accuracy is verified by comparison with recent experiments. By calculating the
ground state in an unrestricted Hartree-Fock approximation and the
collective-mode spectrum in a time-dependent Hartree-Fock approximation, we
construct a phase diagram delimiting regions in the parameter space of the
model where the integer quantum Hall effect occurs in the absence of interlayer
tunneling.Comment: To appear in Phys. Rev. B, 20 pages, 5 PostScript figures uuencoded
with TeX fil
Observation of a Linearly Dispersing Collective Mode in a Quantum Hall Ferromagnet
Double layer two-dimensional electron systems can exhibit a fascinating
collective phase believed to exhibit both quantum ferromagnetism and excitonic
superfluidity. This unusual phase has recently been found to exhibit tunneling
phenomena reminiscent of the Josephson effect. A key element of the theoretical
understanding of this bizarre quantum fluid is the existence of linearly
dispersing Goldstone collective modes. Using the method of tunneling
spectroscopy, we have demonstrated the existence of these modes. We find the
measured velocity to be in reasonable agreement with theoretical estimates.Comment: 5 pages, 4 figures; accepted for publication in PRL. Contains new
data, a new figure, and a new titl
Phase Transition in \nu=2 Bilayer Quantum Hall State
The Hall-plateau width and the activation energy were measured in the bilayer
quantum Hall state at filling factor \nu=2, 1 and 2/3, by changing the total
electron density and the density ratio in the two quantum wells. Their behavior
are remarkably different from one to another. The \nu=1 state is found stable
over all measured range of the density difference, while the \nu=2/3$ state is
stable only around the balanced point. The \nu=2 state, on the other hand,
shows a phase transition between these two types of the states as the electron
density is changed.Comment: 5 pages including figures, RevTe
Who wants to join me? Companion recommendation in location based social networks
We consider the problem of identifying possible companions for a user who is planning to visit a given venue. Specifically, we study the task of predicting which of the user's current friends, in a location based social network (LBSN), are most likely to be interested in joining the visit. An important underlying assumption of our model is that friendship relations can be clustered based on the kinds of interests that are shared by the friends. To identify these friendship types, we use a latent topic model, which moreover takes into account the geographic proximity of the user to the location of the proposed venue. To the best of our knowledge, our model is the first that addresses the task of recommending companions for a proposed activity. While a number of existing topic models can be adapted to make such predictions, we experimentally show that such methods are significantly outperformed by our model
Formation of the First Stars and Quasars
We review observable signatures of the first generation of stars and
low-luminosity quasars, including the metal enrichment, radiation background,
and dust opacity/emission that they produce. We compute the formation history
of collapsed baryonic halos based on an extension of the Press-Schechter
formalism, incorporating the effects of pressure and H2-dissociation, and
calibrate this history to observational data at redshifts z<5. To be consistent
with the lack of faint point-sources in the Hubble Deep Field, we introduce a
lower limit of 75 km/s for the circular velocities of halos harboring central
black holes. Based on our models, we predict that future satellite instruments
such as MAP, Planck, and NGST will be able to detect the signatures small star
clusters and low-luminosity quasars at redshifts exceeding z=10.Comment: 10 pages, 5 figures included. Invited talk at the 32nd COSPAR
Scientific Assemby, 15-17 July, 1998, Nagoya, Japan; to appear in Adv. of
Space Researc
Anisotropy of Magnetoresistance Hysteresis around the Quantum Hall State in Tilted Magnetic Field
We present an anisotropy of the hysteretic transport around the spin
transition point at Landau level filling factor in tilted magnetic
field. When the direction of the in-plane component of the magnetic field
is normal to the probe current , a strong hysteretic
transport due to the current-induced nuclear spin polarization occurs. When
is parallel to , on the other hand, the hysteresis almost
disappears. We also demonstrate that the nuclear spin-lattice relaxation rate
at the transition point increases with decreasing angle between
the directions of and . These results suggest that the
morphology of electron spin domains around is affected by the
current direction.Comment: 4 pages, 4 figure
- âŠ