arXiv subjects

J. Yang

Publications and source records attributed to J. Yang.

At least 73 records · Page 4Linked to original sources

arXiv2023

Commensurate-to-incommensurate transition of charge-density-wave order and a possible quantum critical point in pressurized kagome metal CsV$_3$Sb$_5$

Clarifying the interplay between charge density waves (CDWs) and superconductivity is important in the kagome metal CsV$_3$Sb$_5$, and pressure ($P$) can play a crucial role. Here, we present $^{121/123}$Sb nuclear quadrupole resonance (NQR) measurements under hydrostatic pressures up to 2.43 GPa in CsV$_3$Sb$_5$ single crystals. We demonstrate that the CDW gradually changes from a commensurate modulation with a star-of-David (SoD) pattern to an incommensurate one with a superimposed SoD and Tri-hexagonal (TrH) pattern stacking along the $c$-axis. Moreover, the linewidth $δν$ of $^{121/123}$Sb-NQR spectra increases with cooling down to $T_{\rm CDW}$, indicating the appearance of a short-range CDW order due to CDW fluctuations pinned by quenched disorders. The $δν$ shows a Curie-Weiss temperature dependence and tends to diverge at $P_{\rm c} \sim$ 1.9 GPa, suggesting that a CDW quantum critical point (QCP) exists at $P_{\rm c}$ where $T_{\rm c}$ shows the maximum. For $P > P_{\rm c}$, spin fluctuations are enhanced when the CDW is suppressed. Our results suggest that the maximal $T_{\rm c}$ at $P_{\rm c} \sim$ 1.9 GPa is related to the CDW QCP and the presence of spin fluctuations prevent the $T_{\rm c}$ from a rapid decrease otherwise after the CDW is completely suppressed.

cond-mat.str-el↗

arXiv2022

Multi-wavelength study of the luminous GRB 210619B observed with Fermi and ASIM

We report on detailed multi-wavelength observations and analysis of the very bright and long GRB 210619B, detected by the Atmosphere-Space Interactions Monitor (ASIM) installed on the International Space Station (ISS) and the Gamma-ray Burst Monitor (GBM) on-board the Fermi mission. Our main goal is to understand the radiation mechanisms and jet composition of GRB 210619B. With a measured redshift of $z$ = 1.937, we find that GRB 210619B falls within the 10 most luminous bursts observed by Fermi so far. The energy-resolved prompt emission light curve of GRB 210619B exhibits an extremely bright hard emission pulse followed by softer/longer emission pulses. The low-energy photon indices ($α_{\rm pt}$) values obtained using the time-resolved spectral analysis of the burst suggest a transition between the thermal (during harder pulse) to non-thermal (during softer pulse) outflow. We examine the correlation between spectral parameters and find that both peak energy and $α_{\rm pt}$ exhibit the flux tracking pattern. The late time broadband photometric dataset can be explained within the framework of the external forward shock model with $ν_m$ $< ν_c$ $< ν_{x}$ (where $ν_m$, $ν_c$, and $ν_{x}$ are the synchrotron peak, cooling-break, and X-ray frequencies, respectively) spectral regime supporting a rarely observed hard electron energy index ($p<$ 2). We find moderate values of host extinction of E(B-V) = 0.14 $\pm$ 0.01 mag for the Small Magellanic Cloud (SMC) extinction law. In addition, we also report late-time optical observations with the 10.4 m GTC placing deep upper limits for the host galaxy ($z$=1.937), favouring a faint, dwarf host for the burst.

astro-ph.HE↗

arXiv2022

ADMX-Orpheus First Search for 70 $μ$eV Dark Photon Dark Matter: Detailed Design, Operations, and Analysis

Dark matter makes up 85% of the matter in the universe and 27% of its energy density, but we do not know what comprises dark matter. It is possible that dark matter may be composed of either axions or dark photons, both of which can be detected using an ultra-sensitive microwave cavity known as a haloscope. The haloscope employed by ADMX consists of a cylindrical cavity operating at the TM$_{010}$ mode and is sensitive to the QCD axion with masses of few $μ$eV. However, this haloscope design becomes challenging to implement for higher masses. This is because higher masses require smaller-diameter cavities, consequently reducing the detection volume which diminishes the detected signal power. ADMX-Orpheus mitigates this issue by operating a tunable, dielectrically-loaded cavity at a higher-order mode, allowing the detection volume to remain large. This paper describes the design, operation, analysis, and results of the inaugural ADMX-Orpheus dark photon search between 65.5 $μ$eV (15.8 GHz) and 69.3 $μ$eV (16.8 GHz), as well as future directions for axion searches and for exploring more parameter space.

hep-ex↗

arXiv2022

Search for 70 μeV Dark Photon Dark Matter with a Dielectrically-Loaded Multi-Wavelength Microwave Cavity

Microwave cavities have been deployed to search for bosonic dark matter candidates with masses of a few $μ$eV. However, the sensitivity of these cavity detectors is limited by their volume, and the traditionally-employed half-wavelength cavities suffer from a significant volume reduction at higher masses. ADMX-Orpheus mitigates this issue by operating a tunable, dielectrically-loaded cavity at a higher-order mode, which allows the detection volume to remain large. The ADMX-Orpheus inaugural run excludes dark photon dark matter with kinetic mixing angle $χ> 10^{-13}$ between 65.5 $μ$eV (15.8 GHz) and 69.3 $μ$eV (16.8GHz), marking the highest-frequency tunable microwave cavity dark matter search to date.

hep-ex↗

arXiv2022

Radio interferometric imaging of RS Oph bipolar ejecta for the 2021 nova outburst

The recurrent nova and symbiotic binary RS Oph erupted again in August 2021 for its eighth known outburst. As part of a multi-epoch and frequency campaign, we observed RS Oph 34 days after the outburst at 5 GHz with the European VLBI Network (EVN). The radio image is elongated over the east-west direction for a total extension of about 90 mas (or about 240 AU at the Gaia DR3 distance d=2.68 [-0.15/+0.17] kpc), and shows a bright and compact central component coincident with the Gaia astrometric position, and two lobes east and west of it, expanding perpendicular to the orbital plane. By comparing with the evolution of emission-line profiles on optical spectra, we found the leading edge of the lobes to be expanding at 7550 km/s, and i=54 deg as the orbital inclination of the binary. The 2021 radio structure is remarkably similar to that observed following the 2006 eruption. The obscuring role of the density enhancement on the orbital plane (DEOP) is discussed in connection to the time-dependent visibility of the receding lobe in the background to the DEOP, and the origin of the triple-peaked profiles is traced to the ring structure formed by the nova ejecta impacting the DEOP.

astro-ph.SR↗

arXiv2022

A fast radio burst source at a complex magnetised site in a barred galaxy

Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio bursts. Recent observations of a Galactic FRB suggest that at least some FRBs originate from magnetars, but the origin of cosmological FRBs is still not settled. Here we report the detection of 1863 bursts in 82 hr over 54 days from the repeating source FRB~20201124A. These observations show irregular short-time variation of the Faraday rotation measure (RM), which probes the density-weighted line-of-sight magnetic field strength, of individual bursts during the first 36 days, followed by a constant RM. We detected circular polarisation in more than half of the burst sample, including one burst reaching a high fractional circular polarisation of 75%. Oscillations in fractional linear and circular polarisations as well as polarisation angle as a function of wavelength were detected. All of these features provide evidence for a complicated, dynamically evolving, magnetised immediate environment within about an astronomical unit (au; Earth-Sun distance) of the source. Our optical observations of its Milky-Way-sized, metal-rich host galaxy reveal a barred spiral, with the FRB source residing in a low stellar density, interarm region at an intermediate galactocentric distance. This environment is inconsistent with a young magnetar engine formed during an extreme explosion of a massive star that resulted in a long gamma-ray burst or superluminous supernova.

astro-ph.HE↗

arXiv2022

Interplay of itinerant electrons and Ising moments in a hybrid honeycomb quantum magnet TmNi$_3$Al$_9$

The interplay between itinerant electrons and local magnetic moments in quantum materials brings about rich and fascinating phenomena and stimulates various developments in the theoretical framework. In this work, thermodynamic, electric transport, and neutron diffraction measurements were performed on a newly synthesized honeycomb lattice magnet TmNi$_3$Al$_9$. Based on the experimental data, a magnetic field temperature phase diagram was constructed, exhibiting three essentially different magnetic regions. Below ${T_{\rm N}=2.97 \pm 0.02}\ \rm K$ Tm$^{3+}$ moments order antiferromagnetically in zero field. We found that the Tm$^{3+}$ ions form a pseudo-doublet ground state with the Ising-like moments lying normal to the two-dimensional honeycomb layers. Application of a magnetic field along the easy axis gradually suppresses the antiferromagnetic order in favor of an induced ferromagnetic state above the critical field ${B_c=0.92 \pm 0.05}\ \rm T$. In the vicinity of $B_c$, a strong enhancement of the quantum spin fluctuations was observed. The quantum Ising nature of the local moments and the coupling to itinerant electrons are discussed.

cond-mat.str-el↗

arXiv2022

$E_{\mathrm{iso}}$-$E_{\mathrm{p}}$ correlation of gamma ray bursts: calibration and cosmological applications

Gamma-ray bursts (GRBs) are the most explosive phenomena and can be used to study the expansion of Universe. In this paper, we compile a long GRB sample for the $E_{\mathrm{iso}}$-$E_{\mathrm{p}}$ correlation from Swift and Fermi observations. The sample contains 221 long GRBs with redshifts from 0.03 to 8.20. From the analysis of data in different redshift intervals, we find no statistically significant evidence for the redshift evolution of this correlation. Then we calibrate the correlation in six sub-samples and use the calibrated one to constrain cosmological parameters. Employing a piece-wise approach, we study the redshift evolution of dark energy equation of state (EOS), and find that the EOS tends to be oscillating at low redshift, but consistent with $-1$ at high redshift. It hints a dynamical dark energy at $2σ$ confidence level at low redshift.

astro-ph.HE↗

arXiv2022

Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D$\approx$1.4 Mpc

We report the discovery of Tucana B, an isolated ultra-faint dwarf galaxy at a distance of D=1.4 Mpc. Tucana B was found during a search for ultra-faint satellite companions to the known dwarfs in the outskirts of the Local Group, although its sky position and distance indicate the nearest galaxy to be $\sim$500 kpc distant. Deep ground-based imaging resolves Tucana B into stars, and it displays a sparse red giant branch consistent with an old, metal poor stellar population analogous to that seen in the ultra-faint dwarf galaxies of the Milky Way, albeit at fainter apparent magnitudes. Tucana B has a half-light radius of 80$\pm$40 pc, and an absolute magnitude of $M_V$=$-$6.9$^{+0.5}_{-0.6}$ mag ($L_V$=$(5^{+4}_{-2})\times$10$^4$ $L_{\odot}$), which is again comparable to the Milky Way's ultra-faint satellites. There is no evidence for a population of young stars, either in the optical color magnitude diagram or in GALEX archival ultraviolet imaging, with the GALEX data indicating $\log (\mathrm{SFR_{NUV}/M_\odot \, yr^{-1}}) < -5.4$ for star formation on $\lesssim$100 Myr time scales. Given its isolation and physical properties, Tucana B may be a definitive example of an ultra-faint dwarf that has been quenched by reionization, providing strong confirmation of a key driver of galaxy formation and evolution at the lowest mass scales. It also signals a new era of ultra-faint dwarf galaxy discovery at the extreme edges of the Local Group.

astro-ph.GA↗

arXiv2022

Unveiling the warm dense ISM in $z>6$ quasar host galaxies via water vapor emission

Water vapor (H$_{2}$O) is one of the brightest molecular emitters after carbon monoxide (CO) in galaxies with high infrared (IR) luminosity, and allows us to investigate the warm dense phase of the interstellar medium (ISM) where star formation occurs. However, due to the complexity of its radiative spectrum, H$_{2}$O is not frequently exploited as an ISM tracer in distant galaxies. Therefore, H$_{2}$O studies of the warm and dense gas at high-$z$ remains largely unexplored. In this work we present observations conducted with the Northern Extended Millimeter Array (NOEMA) toward three $z>6$ IR-bright quasars J2310+1855, J1148+5251, and J0439+1634 targeted in their multiple para-/ortho-H$_{2}$O transitions ($3_{12}-3_{03}$, $1_{11}-0_{00}$, $2_{20}-2_{11}$, and $4_{22}-4_{13}$), as well as their far-IR (FIR) dust continuum. By combining our data with previous measurements from the literature we estimate dust masses and temperatures, continuum optical depths, IR luminosities, and the star-formation rates from the FIR continuum. We model the H$_{2}$O lines using the MOLPOP-CEP radiative transfer code and find that water vapor lines in our quasar host galaxies are primarily excited in warm dense (gas kinetic temperature and density of $T_{\rm kin} = 50\,{\rm K}$, $n_{\rm H_{2}}\sim 10^{4.5}-10^{5}\,{\rm cm^{-3}}$) molecular medium with water vapor column density of $N_{\rm H_{2}O}\sim 2\times10^{17}-3\times10^{18}\,{\rm cm^{-3}}$. High-$J$ H$_{2}$O lines are mainly radiatively pumped by the intense optically-thin far-IR radiation field associated with a warm dust component with temperatures of $T_{\rm dust}\sim 80-190\,{\rm K}$ that account for $<5-10\%$ of the total dust mass. Our results are in agreement with expectations based on the H$_{2}$O spectral line energy distribution of local and high-$z$ ultra-luminous IR galaxies and AGN. [abridged]

astro-ph.GA↗

arXiv2022

Widespread, strong outflows in XQR-30 quasars at the Reionisation epoch

Luminous quasars powered by accretion onto billion solar mass black holes already exist at the epoch of Reionisation, when the Universe was 0.5-1 Gyr old. These objects likely reside in over-dense regions of the Universe, and will grow to form today's giant galaxies. How their huge black holes formed in such short times is debated, particularly as they lie above the local black hole mass-galaxy dynamical mass correlation, thus following the black hole-dominance growth path. It is unknown what slowed down the black hole growth, leading towards the symbiotic growth observed in the local Universe, and when this process started, although black hole feedback is a likely driver. This deadlock is due to the lack of large, homogeneous samples of high-redshift quasars with high-quality, broad-band spectroscopic information. Here we report results from a VLT/X-shooter survey of 30 quasars at redshift 5.8$\le$z$\le$6.6 (XQR-30). About 50% of their spectra reveal broad blue-shifted absorption line (BAL) throughs, tracing powerful ionised winds. The BAL fraction in z$\gtrsim$6 quasars is 2-3 times higher than in quasars at z~2-4.5. XQR-30 BAL quasars exhibit extreme outflow velocities, up to 17% of the light speed, rarely observed at lower redshift. These outflows inject large amounts of energy into the galaxy interstellar medium, which can contrast nuclear gas accretion, slowing down the black-hole growth. The star-formation rate in high-z quasar hosts is generally $>$100 M$_\odot$/yr, so these galaxies are growing at a fast rate. The BAL phase may then mark the beginning of significant feedback, acting first on black hole growth and possibly later on galaxy growth. The red optical colors of BAL quasars at z$\gtrsim$6 indeed suggest that these systems are dusty and may be caught during an initial quenching phase of obscured accretion.

astro-ph.GA↗

arXiv2022

A hyper flare of a weeks-old magnetar born from a binary-neutron-star merger

Magnetars, a population of isolated neutron stars with ultra-strong magnetic fields of $\sim 10^{14}-10^{15}$ G, have been increasingly accepted to explain a variety of astrophysical transients. A nascent millisecond-period magnetar can release its spin-down energy and power bright sources such as Gamma-ray Bursts (GRBs) and their subsequent X-ray plateaus, Super Luminous Supernovae (SLSNe), and the fast X-ray transients such as CDF-S XT-2. Magnetars with ages of $10^3-10^4$ years have been observed within the Milky Way Galaxy, which are found to power diverse transients with the expense of their magnetic energy, in the form of giant flares and repeated soft-$γ$-ray or hard X-ray bursts and occasionally fast radio bursts (FRBs). Magnetar giant flares were also detected as disguised short GRBs from nearby galaxies . Here we report the identification of a GRB as a hyper flare of magnetar in a nearby galaxy. The magnitude of the hyper flare is about one thousand times brighter than that of a typical magnetar giant flare. A significant $\sim 80$ millisecond period is detected in the decaying light curve. Interpreting this period as the rotation period and given a magnetic field strength typical for a young magnetar, the age of the magnetar is constrained to be only a few weeks. The non-detection of a (superluminous) supernova nor a GRB weeks before the event further constrains that the magnetar is likely born from an off-axis merger event of two neutron stars. Our finding bridges the gap between the hypothetical millisecond magnetars and the observed Galactic magnetars, and points toward a broader channel of magnetar-powered gamma-ray transients.

astro-ph.HE↗

arXiv2022

Controllable emergent spatial spin modulation in Sr2IrO4 by in situ shear strain

Symmetric anisotropic interaction can be ferromagnetic and antiferromagnetic at the same time but for different crystallographic axes. We show that inducing competition of anisotropic interactions of orthogonal irreducible representations represents a general route to obtain new exotic magnetic states. We demonstrate it here by observing the emergence of a continuously tunable 12-layer spatial spin modulation when distorting the square lattice planes in the quasi-2D antiferromagnetic Sr2IrO4 under in situ shear strain. This translation-symmetry-breaking phase is a result of an unusual strain activated anisotropic interaction which is at the 4th order and competing with the inherent quadratic anisotropic interaction. Such a mechanism of competing anisotropy is distinct from that among the ferromagnetic, antiferromagnetic, and/or the Dzyaloshinskii-Moriya interactions, and it could be widely applicable and highly controllable in low dimensional magnets.

cond-mat.str-el↗

arXiv2022

Multi-wavelength view of the close-by GRB 190829A sheds light on gamma-ray burst physics

Gamma-ray bursts are produced as a result of cataclysmic events such as the collapse of a massive star or the merger of two neutron stars. We monitored the position of the close-by gamma-ray burst GRB~190829A, which originated from a massive star collapse, through very long baseline interferometry (VLBI) observations with the EVN and the VLBA, involving a total of 30 telescopes across 4 continents. We carried out a total of 9 observations between 9 and 117 days after the gamma-ray burst at 5 and 15 GHz, with a typical resolution of few milliarcseconds (mas). We obtained limits on the source size and expansion rate. The limits are in agreement with the size evolution entailed by a detailed modelling of the multi-wavelength light curves with a forward plus reverse shock model, which agrees with the observations across almost 18 orders of magnitude in frequency (including the High Energy Stereoscopic System data at TeV photon energies) and more than 4 orders of magnitude in time. Thanks to the broad, high-cadence coverage of the afterglow, afterglow degeneracies are broken to a large extent, allowing us to capture some unique physical insights: we find a low prompt emission efficiency $\lesssim 10^{-3}$; we constrain the fraction of electrons that are accelerated to relativistic speeds in the forward shock to be $χ_e<13\%$ at the 90\% credible level; we find that the magnetic field energy density in the reverse shock downstream must decay rapidly after the shock crossing. While our model assumes an on-axis jet, our VLBI astrometric measurements alone are not sufficiently tight as to exclude any off-axis viewing angle. On the other hand, we can firmly exclude the line of sight to have been more than $2\,\mathrm{deg}$ away from the border of the region that produced the prompt gamma-ray emission based on compactness arguments.

astro-ph.HE↗

arXiv2022

Possible star-of-David pattern charge density wave with additional modulation in the kagome superconductor CsV$_3$Sb$_5$

$A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) is a novel kagome superconductor coexisting with the charge density wave (CDW) order. Identifying the structure of the CDW order is crucial for understanding the exotic normal state and superconductivity in this system. Here, we report $^{51}$V nuclear magnetic resonance (NMR) and $^{121/123}$Sb nuclear quadrupole resonance (NQR) studies on kagome-metal CsV$_3$Sb$_5$. Below the CDW transition temperature $T_\textrm{CDW} \sim$ 98 K, an abrupt change of spectra was observed, indicating that the transition is of the first order. By further analysing the spectra, we find that the CDW order is commensurate. And most remarkably, the obtained experimental results suggest that the charge modulation of the CDW order is of star-of-David pattern and accompanied by an additional charge modulation in bulk below $T^* \sim$ 40 K. Our results revealing the unconventional CDW order provide new insights into $A$V$_3$Sb$_5$.

cond-mat.supr-con↗

arXiv2022

Mapping the $N = 40$ Island of Inversion: Precision Mass Measurements of Neutron-rich Fe Isotopes

Nuclear properties across the chart of nuclides are key to improving and validating our understanding of the strong interaction in nuclear physics. We present high-precision mass measurements of neutron-rich Fe isotopes performed at the TITAN facility. The multiple-reflection time-of-flight mass spectrometer (MR-ToF-MS), achieving a resolving power greater than $600\,000$ for the first time, enabled the measurement of $^{63-70}$Fe, including first-time high-precision direct measurements ($δm/m \sim 10^{-7}$) of $^{68-70}$Fe, as well as the discovery of a long-lived isomeric state in $^{69}$Fe. These measurements are accompanied by both mean-field and ab initio calculations using the most recent realizations which enable theoretical assignment of the spin-parities of the $^{69}$Fe ground and isomeric states. Together with mean-field calculations of quadrupole deformation parameters for the Fe isotope chain, these results benchmark a maximum of deformation in the $N = 40$ island of inversion in Fe, and shed light on trends in level densities indicated in the newly-refined mass surface.

nucl-ex↗

arXiv2022

Cross-Lingual Text-to-Speech Using Multi-Task Learning and Speaker Classifier Joint Training

In cross-lingual speech synthesis, the speech in various languages can be synthesized for a monoglot speaker. Normally, only the data of monoglot speakers are available for model training, thus the speaker similarity is relatively low between the synthesized cross-lingual speech and the native language recordings. Based on the multilingual transformer text-to-speech model, this paper studies a multi-task learning framework to improve the cross-lingual speaker similarity. To further improve the speaker similarity, joint training with a speaker classifier is proposed. Here, a scheme similar to parallel scheduled sampling is proposed to train the transformer model efficiently to avoid breaking the parallel training mechanism when introducing joint training. By using multi-task learning and speaker classifier joint training, in subjective and objective evaluations, the cross-lingual speaker similarity can be consistently improved for both the seen and unseen speakers in the training set.

cs.SD↗

arXiv2022

Antiferromagnetic Excitonic Insulator State in Sr3Ir2O7

Excitonic insulators are usually considered to form via the condensation of a soft charge mode of bound electron-hole pairs. This, however, presumes that the soft exciton is of spin-singlet character. Early theoretical considerations have also predicted a very distinct scenario, in which the condensation of magnetic excitons results in an antiferromagnetic excitonic insulator state. Here we report resonant inelastic x-ray scattering (RIXS) measurements of Sr3Ir2O7. By isolating the longitudinal component of the spectra, we identify a magnetic mode that is well-defined at the magnetic and structural Brillouin zone centers, but which merges with the electronic continuum in between these high-symmetry points and which decays upon heating concurrent with a decrease in the material's resistivity. We show that a bilayer Hubbard model, in which electron-hole pairs are bound by exchange interactions, consistently explains all the electronic and magnetic properties of Sr3Ir2O7 indicating that this material is a realization of the long-predicted antiferromagnetic excitonic insulators phase.

cond-mat.str-el↗