710 research outputs found
Quantum oscillations from Fermi arcs
When a metal is subjected to strong magnetic field B nearly all measurable
quantities exhibit oscillations periodic in 1/B. Such quantum oscillations
represent a canonical probe of the defining aspect of a metal, its Fermi
surface (FS). In this study we establish a new mechanism for quantum
oscillations which requires only finite segments of a FS to exist. Oscillations
periodic in 1/B occur if the FS segments are terminated by a pairing gap. Our
results reconcile the recent breakthrough experiments showing quantum
oscillations in a cuprate superconductor YBCO, with a well-established result
of many angle resolved photoemission (ARPES) studies which consistently
indicate "Fermi arcs" -- truncated segments of a Fermi surface -- in the normal
state of the cuprates.Comment: 8 pages, 5 figure
Energy gaps in the failed high-Tc superconductor La1.875Ba0.125CuO4
A central issue on high-Tc superconductivity is the nature of the
normal-state gap (pseudogap) in the underdoped regime and its relationship with
superconductivity. Despite persistent efforts, theoretical ideas for the
pseudogap evolve around fluctuating superconductivity, competing order and
spectral weight suppression due to many-body effects. Recently, while some
experiments in the superconducting state indicate a distinction between the
superconducting gap and pseudogap, others in the normal state, either by
extrapolation from high-temperature data or directly from La1.875Ba0.125CuO4
(LBCO-1/8) at low temperature, suggest the ground-state pseudogap is a single
gap of d-wave form. Here we report angle-resolved photoemission (ARPES) data
from LBCO-1/8, collected with improved experimental conditions, that reveal the
ground-state pseudogap has a pronounced deviation from the simple d-wave form.
It contains two distinct components: a d-wave component within an extended
region around the node and the other abruptly enhanced close to the antinode,
pointing to a dual nature of the pseudogap in this failed high-Tc
superconductor which involves a possible precursor pairing energy scale around
the node and another of different but unknown origin near the antinode.Comment: Nature Physics advance online publication, Dec. 21st 2008; Author's
original version of the main text; for a better resolution of figures &
Supplementary Information, visit Nature Physics' websit
A Search for Neutrinos from the Solar hep Reaction and the Diffuse Supernova Neutrino Background with the Sudbury Neutrino Observatory
A search has been made for neutrinos from the hep reaction in the Sun and from the diffus
Computer-tailored dietary behaviour change interventions: a systematic review
Improving dietary behaviours such as increasing fruit and vegetable consumption and reducing saturated fat intake are important in the promotion of better health. Computer tailoring has shown promise as a strategy to promote such behaviours. A narrative systematic review was conducted to describe the available evidence on ‘second’-generation computer-tailored primary prevention interventions for dietary behaviour change and to determine their effectiveness and key characteristics of success. Systematic literature searches were conducted through five databases: Medline, Embase, PsycINFO, CINAHL and All EBM Reviews and by examining the reference lists of relevant articles to identify studies published in English from January 1996 to 2008. Randomized controlled trials or quasi-experimental designs with pre-test and post-test behavioural outcome data were included. A total of 13 articles were reviewed, describing the evaluation of 12 interventions, seven of which found significant positive effects of the computer-tailored interventions for dietary behaviour outcomes, one also for weight reduction outcomes. Although the evidence of short-term efficacy for computer-tailored dietary behaviour change interventions is fairly strong, the uncertainty lies in whether the reported effects are generalizable and sustained long term. Further research is required to address these limitations of the evidence
Measurement of the Total Active 8B Solar Neutrino Flux at the Sudbury Neutrino Observatory with Enhanced Neutral Current Sensitivity
The Sudbury Neutrino Observatory (SNO) has precisely determined the total
active (nu_x) 8B solar neutrino flux without assumptions about the energy
dependence of the nu_e survival probability. The measurements were made with
dissolved NaCl in the heavy water to enhance the sensitivity and signature for
neutral-current interactions. The flux is found to be 5.21 +/- 0.27 (stat) +/-
0.38 (syst) x10^6 cm^{-2}s^{-1}, in agreement with previous measurements and
standard solar models. A global analysis of these and other solar and reactor
neutrino results yields Delta m^{2} = 7.1^{+1.2}_{-0.6}x10^{-5} ev^2 and theta
= 32.5^{+2.4}_{-2.3} degrees. Maximal mixing is rejected at the equivalent of
5.4 standard deviations.Comment: Submitted to Phys. Rev. Let
Germline Analysis from Tumor–Germline Sequencing Dyads to Identify Clinically Actionable Secondary Findings
To evaluate germline variants in hereditary cancer susceptibility genes among unselected cancer patients undergoing tumor-germline sequencing
Progress in Neutron Scattering Studies of Spin Excitations in High-Tc Cuprates
Neutron scattering experiments continue to improve our knowledge of spin
fluctuations in layered cuprates, excitations that are symptomatic of the
electronic correlations underlying high-temperature superconductivity.
Time-of-flight spectrometers, together with new and varied single crystal
samples, have provided a more complete characterization of the magnetic energy
spectrum and its variation with carrier concentration. While the spin
excitations appear anomalous in comparison with simple model systems, there is
clear consistency among a variety of cuprate families. Focusing initially on
hole-doped systems, we review the nature of the magnetic spectrum, and
variations in magnetic spectral weight with doping. We consider connections
with the phenomena of charge and spin stripe order, and the potential
generality of such correlations as suggested by studies of magnetic-field and
impurity induced order. We contrast the behavior of the hole-doped systems with
the trends found in the electron-doped superconductors. Returning to hole-doped
cuprates, studies of translation-symmetry-preserving magnetic order are
discussed, along with efforts to explore new systems. We conclude with a
discussion of future challenges.Comment: revised version, to be published in JPSJ, 20 pages, 21 figure
Measurement of the rate of nu_e + d --> p + p + e^- interactions produced by 8B solar neutrinos at the Sudbury Neutrino Observatory
Solar neutrinos from the decay of B have been detected at the Sudbury
Neutrino Observatory (SNO) via the charged current (CC) reaction on deuterium
and by the elastic scattering (ES) of electrons. The CC reaction is sensitive
exclusively to nu_e's, while the ES reaction also has a small sensitivity to
nu_mu's and nu_tau's. The flux of nu_e's from ^8B decay measured by the CC
reaction rate is
\phi^CC(nu_e) = 1.75 +/- 0.07 (stat)+0.12/-0.11 (sys.) +/- 0.05(theor) x 10^6
/cm^2 s.
Assuming no flavor transformation, the flux inferred from the ES reaction
rate is
\phi^ES(nu_x) = 2.39+/-0.34 (stat.)+0.16}/-0.14 (sys) x 10^6 /cm^2 s.
Comparison of \phi^CC(nu_e) to the Super-Kamiokande Collaboration's precision
value of \phi^ES(\nu_x) yields a 3.3 sigma difference, providing evidence that
there is a non-electron flavor active neutrino component in the solar flux. The
total flux of active ^8B neutrinos is thus determined to be 5.44 +/-0.99 x
10^6/cm^2 s, in close agreement with the predictions of solar models.Comment: 6 pages (LaTex), 3 figures, submitted to Phys. Rev. Letter
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