100 research outputs found
Resonant X-Ray Scattering Investigations of Charge Density Wave and Nematic Orders in Cuprate Superconductors
In the cuprate superconductors, superconductivity often co-exists with other
types of order, including charge density wave and nematic orders. Over the past
decade, resonant x-ray scattering has emerged as a key tool to investigate
these competing/coexisting orders, providing valuable insights into their
microscopic character. In this report we provide a brief review of the
technique and highlight selected recent advances in study charge density wave
order and nematic order in the cuprates.Comment: 12 pages, 6 figure
Angular Fluctuations of a Multicomponent Order Describe the Pseudogap of
The hole-doped cuprate high-temperature superconductors enter the pseudogap regime as their superconducting critical temperature, , falls with decreasing hole density. Recent x-ray scattering experiments in observe incommensurate charge-density wave fluctuations whose strength rises gradually over a wide temperature range above , but then decreases as the temperature is lowered below . We propose a theory in which the superconducting and charge-density wave orders exhibit angular fluctuations in a six-dimensional space. The theory provides a natural quantitative fit to the x-ray data and can be a basis for understanding other characteristics of the pseudogap.Physic
Harnessing optical micro-combs for microwave photonics
In the past decade, optical frequency combs generated by high-Q
micro-resonators, or micro-combs, which feature compact device footprints, high
energy efficiency, and high-repetition-rates in broad optical bandwidths, have
led to a revolution in a wide range of fields including metrology, mode-locked
lasers, telecommunications, RF photonics, spectroscopy, sensing, and quantum
optics. Among these, an application that has attracted great interest is the
use of micro-combs for RF photonics, where they offer enhanced functionalities
as well as reduced size and power consumption over other approaches. This
article reviews the recent advances in this emerging field. We provide an
overview of the main achievements that have been obtained to date, and
highlight the strong potential of micro-combs for RF photonics applications. We
also discuss some of the open challenges and limitations that need to be met
for practical applications.Comment: 32 Pages, 13 Figures, 172 Reference
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Diamagnetism and density-wave order in the pseudogap regime of YBa 2 Cu 3 O 6 + x
Clear experimental evidence of charge density-wave correlations competing with superconducting order in YBCO have thrust their relationship with the pseudogap regime into the spotlight. To aid in characterizing the pseudogap regime, we propose a dimensionless ratio of the diamagnetic susceptibility to the correlation length of the charge density-wave correlations. Using Monte Carlo simulations, we compute this ratio on the classical model of Hayward et al. [Science 343, 1336 (2014)], which describes angular fluctuations of a multicomponent order, capturing both superconducting and density-wave correlations. We compare our results with available data on YBa2Cu3O6+x, and propose experiments to clarify the value of this dimensionless ratio using existing samples and techniques.Physic
Globular Cluster and Galaxy Formation: M31, the Milky Way and Implications for Globular Cluster Systems of Spiral Galaxies
The globular cluster (GC) systems of the Milky Way and of our neighboring
spiral galaxy, M31, comprise 2 distinct entities, differing in 3 respects. 1.
M31 has young GCs, ages from ~100 Myr to 5 Gyr old, as well as old globular
clusters. No such young GCs are known in the Milky Way. 2. We confirm that the
oldest M31 GCs have much higher nitrogen abundances than do Galactic GCs at
equivalent metallicities. 3. Morrison et al. found M31 has a subcomponent of
GCs that follow closely the disk rotation curve of M31. Such a GC system in our
own Galaxy has yet to be found. These data are interpreted in terms of the
hierarchical-clustering-merging (HCM) paradigm for galaxy formation. We infer
that M31 has absorbed more of its dwarf systems than has the Milky Way. This
inference has 3 implications: 1. All spiral galaxies likely differ in their GC
properties, depending on how many companions each galaxy has, and when the
parent galaxy absorbs them. The the Milky Way ties down one end of this
spectrum, as almost all of its GCs were absorbed 10-12 Gyr ago. 2. It suggests
that young GCs are preferentially formed in the dwarf companions of parent
galaxies, and then absorbed by the parent galaxy during mergers. 3. Young GCs
seen in tidally-interacting galaxies might come from dwarf companions of these
galaxies, rather than be made a-new in the tidal interaction. There is no ready
explanation for the marked difference in nitrogen abundance for old M31 GCs
relative to the oldest Galactic GCs. The predictions made by Li & Burstein
regarding the origin of nitrogen abundance in globular clusters are consistent
with what is found for the old M31 GCs compared to that for the two 5 Gyr-old
M31 GCs.Comment: to be published in ApJ, Oct 2004; 13 pages of text, 2 tables, 7
postscript figure
Six supersoft X-ray binaries: system parameters and twin-jet outflows
A comparison is made between the properties of CAL 83, CAL 87, RX
J0513.9-6951, 1E 0035.4-7230 (SMC 13), RX J0019.8+2156, and RX J0925.7-4758,
all supersoft X-ray binaries. Spectra with the same resolution and wavelength
coverage of these systems are compared and contrasted. Some new photometry is
also presented. The equivalent widths of the principal emission lines of H and
He II differ by more than an order of magnitude among these sources, although
those of the highest ionization lines (e.g. O VI) are very similar. In
individual systems, the velocity curves derived from various ions often differ
in phasing and amplitude, but those whose phasing is consistent with the light
curves (implying the lines are formed near the compact star) give masses of
and for the degenerate and mass-losing
stars, respectively. This finding is in conflict with currently prevailing
theoretical models for supersoft binaries. The three highest luminosity sources
show evidence of "jet" outflows, with velocities of .
In CAL 83 the shape of the He II 4686\AA profile continues to show evidence
that these jets may precess with a period of days.Comment: 27 pages including 5 tables, plus 6 figures. To appear in Ap
Tracing PAHs and Warm Dust Emission in the Seyfert Galaxy NGC 1068
We present a study of the nearby Seyfert galaxy NGC 1068 using mid- and far-
infrared data acquired with the IRAC, IRS, and MIPS instruments aboard the
Spitzer Space Telescope. The images show extensive 8 um and 24 um emission
coinciding with star formation in the inner spiral approximately 15" (1 kpc)
from the nucleus, and a bright complex of star formation 47" (3 kpc) SW of the
nucleus. The brightest 8 um PAH emission regions coincide remarkably well with
knots observed in an Halpha image. Strong PAH features at 6.2, 7.7, 8.6, and
11.3 um are detected in IRS spectra measured at numerous locations inside,
within, and outside the inner spiral. The IRAC colors and IRS spectra of these
regions rule out dust heated by the AGN as the primary emission source; the
SEDs are dominated by starlight and PAH emission. The equivalent widths and
flux ratios of the PAH features in the inner spiral are generally consistent
with conditions in a typical spiral galaxy ISM. Interior to the inner spiral,
the influence of the AGN on the ISM is evident via PAH flux ratios indicative
of a higher ionization parameter and a significantly smaller mean equivalent
width than observed in the inner spiral. The brightest 8 and 24 um emission
peaks in the disk of the galaxy, even at distances beyond the inner spiral, are
located within the ionization cones traced by [O III]/Hbeta, and they are also
remarkably well aligned with the axis of the radio jets. Although it is
possible that radiation from the AGN may directly enhance PAH excitation or
trigger the formation of OB stars that subsequently excite PAH emission at
these locations in the inner spiral, the orientation of collimated radiation
from the AGN and star formation knots in the inner spiral could be
coincidental. (abridged)Comment: 20 pages, 11 figures; AJ, accepted; full resolution version available
at http://spider.ipac.caltech.edu/staff/jhhowell/astro/howelln1068.pd
The K2-HERMES Survey: Age and Metallicity of the Thick Disc
Asteroseismology is a promising tool to study Galactic structure and
evolution because it can probe the ages of stars. Earlier attempts comparing
seismic data from the {\it Kepler} satellite with predictions from Galaxy
models found that the models predicted more low-mass stars compared to the
observed distribution of masses. It was unclear if the mismatch was due to
inaccuracies in the Galactic models, or the unknown aspects of the selection
function of the stars. Using new data from the K2 mission, which has a
well-defined selection function, we find that an old metal-poor thick disc, as
used in previous Galactic models, is incompatible with the asteroseismic
information. We show that spectroscopic measurements of [Fe/H] and
[/Fe] elemental abundances from the GALAH survey indicate a mean
metallicity of for the thick disc. Here is the
effective solar-scaled metallicity, which is a function of [Fe/H] and
[/Fe]. With the revised disc metallicities, for the first time, the
theoretically predicted distribution of seismic masses show excellent agreement
with the observed distribution of masses. This provides an indirect
verification of the asteroseismic mass scaling relation is good to within five
percent. Using an importance-sampling framework that takes the selection
function into account, we fit a population synthesis model of the Galaxy to the
observed seismic and spectroscopic data. Assuming the asteroseismic scaling
relations are correct, we estimate the mean age of the thick disc to be about
10 Gyr, in agreement with the traditional idea of an old -enhanced
thick disc.Comment: 21 pages, submitted to MNRA
The GALAH survey: Properties of the Galactic disc(s) in the solar neighbourhood
Using data from the GALAH pilot survey, we determine properties of the Galactic thin and thick discs near the solar neighbourhood. The data cover a small range of Galactocentric radius (7.9 RGC 9.5 kpc), but extend up to 4 kpc in height from the Galactic plane, and several kpc in the direction of Galactic anti-rotation (at longitude 260⊠††280âŠ). This allows us to reliably measure the vertical density and abundance profiles of the chemically and
kinematically defined âthickâ and âthinâ discs of the Galaxy. The thin disc (low-α population) exhibits a steep negative vertical metallicity gradient, at d[M/H]/dz = â0.18 ± 0.01 dex kpcâ1, which is broadly consistent with previous studies. In contrast, its vertical α-abundance profile is almost flat, with a gradient of d[α/M]/dz = 0.008 ± 0.002 dex kpcâ1. The steep vertical metallicity gradient of the low-α population is in agreement with models where radial
migration has a major role in the evolution of the thin disc. The thick disc (high-α population) has a weaker vertical metallicity gradient d[M/H]/dz = â0.058 ± 0.003 dex kpcâ1. The αabundance of the thick disc is nearly constant with height, d[α/M]/dz = 0.007 ± 0.002 dex kpcâ1. The negative gradient in metallicity and the small gradient in [α/M] indicate that the high-α population experienced a settling phase, but also formed prior to the onset of major
Type Ia supernova enrichment. We explore the implications of the distinct α-enrichments and narrow [α/M] range of the sub-populations in the context of thick disc formation.LD and MA acknowledge funding from the Australian Government through ARC Laureate Fellowship FL110100012. LD, KCF, and RFGW acknowledge
support from ARC grant DP160103747. LC gratefully acknowledges support from the Australian Research Council (grants
DP150100250, FT160100402). DMN was supported by the Allan C. and Dorothy H. Davis Fellowship. DS is the recipient of
an Australian Research Council Future Fellowship (project number
FT1400147). TZ acknowledges financial support from the Slovenian Research Agency (research core funding No. P1-0188). Part of
this research was supported by the Munich Institute for Astro- and
Particle Physics (MIAPP) of the DFG cluster of excellence âOrigin
and Structure of the Universeâ
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