136 research outputs found
Singular charge fluctuations at a magnetic quantum critical point
Strange metal behavior is ubiquitous in correlated materials, ranging from cuprate superconductors to bilayer graphene, and may arise from physics beyond the quantum fluctuations of a Landau order parameter. In quantum-critical heavy-fermion antiferromagnets, such physics may be realized as critical Kondo entanglement of spin and charge and probed with optical conductivity. We present terahertz time-domain transmission spectroscopy on molecular beam epitaxy–grown thin films of YbRh2Si2, a model strange-metal compound. We observed frequency over temperature scaling of the optical conductivity as a hallmark of beyond-Landau quantum criticality. Our discovery suggests that critical charge fluctuations play a central role in the strange metal behavior, elucidating one of the long-standing mysteries of correlated quantum matter.Financial support for this work was provided by the European Research Council (ERC Advanced Grant 227378), the U.S. Army Research Office (ARO W911NF-14-1-0496), the Austrian Science Fund (FWF W1243, P29279-N27, and P29296-N27), and the European Union’s Horizon 2020 research and innovation programme (grant agreement No 824109 – EMP). X.L. and J.K. acknowledge financial support from the National Science Foundation (NSF MRSEC DMR-1720595) and the ARO (W911NF-17-1-0259). Q.S. acknowledges financial support from the NSF (DMR-1920740), the Robert A.Welch Foundation (C-1411), and the ARO (W911NF-14-1-0525), and hospitality of the University of California at Berkeley, the Aspen Center for Physics (NSF grant PHY-1607611), and the Los Alamos National Laboratory (via a Ulam Scholarship from the Center for Nonlinear Studies). This work has also been supported by an InterDisciplinary Excellence Award (IDEA) from Rice University (Q.S., E.R., J.K., S.P.)
Singular charge fluctuations at a magnetic quantum critical point
Strange metal behavior is ubiquitous in correlated materials, ranging from cuprate superconductors to bilayer graphene, and may arise from physics beyond the quantum fluctuations of a Landau order parameter. In quantum-critical heavy-fermion antiferromagnets, such physics may be realized as critical Kondo entanglement of spin and charge and probed with optical conductivity. We present terahertz time-domain transmission spectroscopy on molecular beam epitaxy–grown thin films of YbRh₂Si₂, a model strange-metal compound. We observed frequency over temperature scaling of the optical conductivity as a hallmark of beyond-Landau quantum criticality. Our discovery suggests that critical charge fluctuations play a central role in the strange metal behavior, elucidating one of the long-standing mysteries of correlated quantum matter
A contemporaneous infrared flash from a long gamma-ray burst: an echo from the central engine
The explosion that results in a cosmic gamma-ray burst (GRB) is thought to
produce emission from two physical processes -- the activity of the central
engine gives rise to the high-energy emission of the burst through internal
shocking and the subsequent interaction of the flow with the external
environment produces long-wavelength afterglow. While afterglow observations
continue to refine our understanding of GRB progenitors and relativistic
shocks, gamma-ray observations alone have not yielded a clear picture of the
origin of the prompt emission nor details of the central engine. Only one
concurrent visible-light transient has been found and was associated with
emission from an external shock. Here we report the discovery of infrared (IR)
emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of
GRB 041219a. Our robotic telescope acquired 21 images during the active phase
of the burst, yielding the earliest multi-colour observations of any
long-wavelength emission associated with a GRB. Analysis of an initial IR pulse
suggests an origin consistent with internal shocks. This opens a new
possibility to study the central engine of GRBs with ground-based observations
at long wavelengths.Comment: Accepted to Nature on March 1, 2005. 9 pages, 4 figures, nature12.cls
and nature1.cls files included. This paper is under press embargo until print
publicatio
Singular charge fluctuations at a magnetic quantum critical point
Strange metal behavior is ubiquitous in correlated materials, ranging from cuprate superconductors to bilayer graphene, and may arise from physics beyond the quantum fluctuations of a Landau order parameter. In quantum-critical heavy-fermion antiferromagnets, such physics may be realized as critical Kondo entanglement of spin and charge and probed with optical conductivity. We present terahertz time-domain transmission spectroscopy on molecular beam epitaxy–grown thin films of YbRh2Si2, a model strange-metal compound. We observed frequency over temperature scaling of the optical conductivity as a hallmark of beyond-Landau quantum criticality. Our discovery suggests that critical charge fluctuations play a central role in the strange metal behavior, elucidating one of the long-standing mysteries of correlated quantum matter
X-raying the Intergalactic OVI Absorbers
The observed intergalactic OVI absorbers at z>0 have been regarded as a
significant reservoir of the ``missing baryons''. However, to fully understand
how these absorbers contribute to the baryon inventory, it is crucial to
determine whether the systems are collisionally ionized or photoionized (or
both). Using the identified intergalactic OVI absorbers as tracers, we search
for the corresponding X-ray absorption lines, which are useful for finding the
missing baryons and for revealing the nature of the OVI absorbers. Stacking the
Chandra grating spectra along six AGN sight lines, we obtain three spectra with
signal-to-noise ratios of 32, 28, and 10 per 12.5 mA spectral bin around the
expected OVII Kalpha wavelength. These spectra correspond to OVI absorbers with
various dynamic properties. We find no detectable NeIX, OVII, OVIII, NVII, or
CVI absorption lines in the spectra, but the high counting statistics allows us
to obtain firm upper limits on the corresponding ionic column densities (in
particular N(OVII)<=10 N(OVI) on average at the 95% confidence level). Jointly
analyzing these non-detected X-ray lines with the averaged OVI column density,
we further limit the average temperature of the OVI-bearing gas to be
log[T(K)]<=5.7 in collisional ionization equilibrium. We discuss the
implications of these results for physical properties of the putative warm-hot
intergalactic medium and its detection in future X-ray observations.Comment: 10 pages, 6 figures, 3 tables; minor changes following referee's
comments; Accepted for publication in Ap
The Circumgalactic Medium in Massive Halos
This chapter presents a review of the current state of knowledge on the cool
(T ~ 1e4 K) halo gas content around massive galaxies at z ~ 0.2-2. Over the
last decade, significant progress has been made in characterizing the cool
circumgalactic gas in massive halos of Mh ~ 1e12-1e14 Msun at intermediate
redshifts using absorption spectroscopy. Systematic studies of halo gas around
massive galaxies beyond the nearby universe are made possible by large
spectroscopic samples of galaxies and quasars in public archives. In addition
to accurate and precise constraints for the incidence of cool gas in massive
halos, detailed characterizations of gas kinematics and chemical compositions
around massive quiescent galaxies at z ~ 0.5 have also been obtained. Combining
all available measurements shows that infalling clouds from external sources
are likely the primary source of cool gas detected at d >~ 100 kpc from massive
quiescent galaxies. The origin of the gas closer in is currently less certain,
but SNe Ia driven winds appear to contribute significantly to cool gas found at
d < 100 kpc. In contrast, cool gas observed at d <~ 200 kpc from luminous
quasars appears to be intimately connected to quasar activities on parsec
scales. The observed strong correlation between cool gas covering fraction in
quasar host halos and quasar bolometric luminosity remains a puzzle. Combining
absorption-line studies with spatially-resolved emission measurements of both
gas and galaxies is the necessary next step to address remaining questions.Comment: 29 pages, 7 figures, invited review to appear in "Gas Accretion onto
Galaxies", Astrophysics and Space Science Library, eds. A. Fox & R. Dave, to
be published by Springe
An efficacy trial of brief lifestyle intervention delivered by generalist community nurses (CN SNAP trial)
<p>Abstract</p> <p>Background</p> <p>Lifestyle risk factors, in particular smoking, nutrition, alcohol consumption and physical inactivity (SNAP) are the main behavioural risk factors for chronic disease. Primary health care (PHC) has been shown to be an effective setting to address lifestyle risk factors at the individual level. However much of the focus of research to date has been in general practice. Relatively little attention has been paid to the role of nurses working in the PHC setting. Community health nurses are well placed to provide lifestyle intervention as they often see clients in their own homes over an extended period of time, providing the opportunity to offer intervention and enhance motivation through repeated contacts. The overall aim of this study is to evaluate the impact of a brief lifestyle intervention delivered by community nurses in routine practice on changes in clients' SNAP risk factors.</p> <p>Methods/Design</p> <p>The trial uses a quasi-experimental design involving four generalist community nursing services in NSW Australia. Services have been randomly allocated to an 'early intervention' group or 'late intervention' (comparison) group. 'Early intervention' sites are provided with training and support for nurses in identifying and offering brief lifestyle intervention for clients during routine consultations. 'Late intervention site' provide usual care and will be offered the study intervention following the final data collection point. A total of 720 generalist community nursing clients will be recruited at the time of referral from participating sites. Data collection consists of 1) telephone surveys with clients at baseline, three months and six months to examine change in SNAP risk factors and readiness to change 2) nurse survey at baseline, six and 12 months to examine changes in nurse confidence, attitudes and practices in the assessment and management of SNAP risk factors 3) semi-structured interviews/focus with nurses, managers and clients in 'early intervention' sites to explore the feasibility, acceptability and sustainability of the intervention.</p> <p>Discussion</p> <p>The study will provide evidence about the effectiveness and feasibility of brief lifestyle interventions delivered by generalist community nurses as part of routine practice. This will inform future community nursing practice and PHC policy.</p> <p>Trial Registration</p> <p>ACTRN12609001081202</p
An In-depth Appraisal of Career Termination Experiences in Professional Cricket
This qualitative study explored the career termination experiences of 9 male, retired professional cricketers, between the ages of 28 to 40 (M = 34, SD = 4.65). The participants took part in retrospective, semi-structured interviews. Data from the interviews were inductively content analysed within three transition phases of the retirement process: reasons for retirement, factors affecting adaptation, and reactions to retirement. The reasons for retirement were multicausal with the majority of the participants highlighting contractual pressures and a lack of communication as important precursors to retirement. Three main themes accounted for the factors affecting adaptation: a limited pursuit of other interests, developmental experiences and coping strategies. In terms of reactions to retirement, all of the participants reflected negatively on the termination of their career, with a sense of loss and resentment characterising the post-retirement period. The findings illustrated the sport-specific nature of career termination in professional cricket, and added further support to the emerging consensus that the distinction between voluntary and involuntary retirement is, at best, unclear
Detecting the warm-hot intergalactic medium through X-ray absorption lines
The warm-hot intergalactic medium (WHIM) at temperatures 1E5-1E7 K is
believed to contain 30-50% of the baryons in the local universe. However, all
current X-ray detections of the WHIM at redshifts z>0 are of low statistical
significance (<=3sigma) and/or controversial. In this work, we aim to establish
the detection limits of current X-ray observatories and explore requirements
for next-generation X-ray telescopes for studying the WHIM through X-ray
absorption lines. We analyze all available grating observations of Mrk 421 and
obtain spectra with signal-to-noise ratio (S/N) of \sim90 and 190 per 50 mA
spectral bin from Chandra and XMM observations, respectively. Although these
spectra are two of the best ever collected with Chandra and XMM, we cannot
confirm the two WHIM systems reported by Nicastro et al. in 2005. Our bootstrap
simulations indicate that spectra with such high S/N cannot constrain the WHIM
with OVII column densities N(OVII)\sim1e15 cm^{-2} (corresponding to an
equivalent widths of 2.5 mA for a Doppler velocity of 50 km s^{-1}) at >=3sigma
significance level. The simulation results also suggest that it would take >60
Ms for Chandra and 140 Ms for XMM to measure the N(OVII) at >=4sigma from a
spectrum of a background QSO with flux of \sim0.2 mCrab (1 Crab = 2E-8 erg
s^{-1} cm^{-2} at 0.5-2 keV). Future X-ray pectrographs need to be equipped
with spectral resolution R \sim 4000 and effective area A>=100 cm^2 to
accomplish the similar constraints with an exposure time of \sim2 Ms and would
require \sim11 Ms to survey the 15 QSOs with flux \sim0.2 mCrab along which
clear intergalactic OVI absorbers have been detected.Comment: 13 pages with 9 figures and 2 tables, accepted for publication in Ap
A Compiled Catalogue of Spectroscopically Determined Elemental Abundances for Stars with Accurate Parallaxes. I.Magnesium
We present a compiled catalogue of effective temperatures, surface gravities,
iron and magnesium abundances, distances, velocity components, and orbital
elements for stars in the solar neighborhood. The atmospheric parameters and
iron abundances are averages of published values derived from model synthetic
spectra for a total of about 2000 values in 80 publications. Our relative
magnesium abundances were found from 1412 values in 31 publications for 876
dwarfs and subgiants using a three-step iteration averaging procedure, with
weights assigned to each source of data as well as to each individual
determination and taking into account systematic deviations of each scale
relative to the reduced mean scale. The estimated assumed completeness for data
sources containing more than five stars, up to late December 2003, exceeds 90%.
For the vast majority of stars in the catalogue, the spatial velocity
components were derived from modern high-precision astrometric observations,
and their Galactic orbit elements were computed using a three-component model
of the Galaxy, consisting of a disk, a bulge, and a massive extended halo.Comment: Accepted for Astron. Rep. 2005, v.49, No.5, p.405-416, 12 pages, 10
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