arXiv subjects

Y. Peng

Publications and source records attributed to Y. Peng.

At least 19 recordsLinked to original sources

arXiv2026

Beam-Tracing-Based Quantitative Reconstruction of Density Fluctuations in QUEST Using Doppler Backscattering

A three-channel X-/Ku-band Doppler backscattering (DBS) system has been developed and installed on QUEST for turbulence and electric-field measurements. In spherical tokamaks, the large magnetic-field pitch angle increases the geometric mismatch between the probing beam wave vector and the local magnetic-field vector, reducing the effective perpendicular projection and resulting in a systematic underestimation of the measured scattering intensity. In addition, in QUEST, where low plasma density requires a low-frequency probe beam, beam propagation effects become increasingly significant, further complicating the interpretation of the measured DBS power in terms of local density fluctuation amplitude. To address these issues, a quantitative correction methodology based on the synthetic DBS code SCOTTY was established. All relevant diagnostic response effects were evaluated using SCOTTY along ray trajectories, yielding a correction factor for reconstructing the local turbulence amplitude from the measured scattering signal. The correction factor exhibits strong spatial and frequency dependence, varying by up to an order of magnitude between the plasma core and edge regions, highlighting the necessity of frequency-dependent corrections. By applying the derived correction factor to experimental measurements, quantitative density fluctuation amplitudes were reconstructed from the detected scattering signals. Evaluation of the fluctuation amplitude indicates enhanced turbulence activity in the plasma edge region, where a finite negative radial electric field is inferred. This work demonstrates the first quantitative turbulence evaluation using low-frequency X-/Ku-band DBS measurements in QUEST and establishes a framework for quantitative DBS analysis in spherical tokamaks.

physics.plasm-ph↗

arXiv2026

The MAGPI Survey: Evidence for Non-Universal Resolved Dust Attenuation Relations Beyond the Local Universe

We study the spatially resolved relation between dust attenuation ($A_V$) and star formation rate surface density ($\Sigma_{\mathrm{SFR}}$) in galaxies from the MAGPI survey ($0.25 < z < 0.42$). Using Balmer-decrement-based attenuation maps for 178 galaxies, we investigate whether the locally calibrated resolved $A_V$--$\Sigma_{\mathrm{SFR}}$ relation remains valid at intermediate redshift by comparing MAGPI with the local relation measured from MaNGA. We find a clear positive correlation between $A_V$ and $\Sigma_{\mathrm{SFR}}$ in MAGPI, with systematically higher attenuation than in MaNGA at fixed $\Sigma_{\mathrm{SFR}}$. After matching galaxies in stellar mass ($M_{*}$) and offset from the star-forming main sequence ($\Delta$SFMS), MAGPI galaxies remain more attenuated than MaNGA galaxies at fixed $\Sigma_{\mathrm{SFR}}$. The attenuation excess is strongest for galaxies below the SFMS ($\Delta A_V \sim 0.40$ mag), weaker for galaxies on the SFMS ($\Delta A_V \sim 0.28$ mag), and minimal for galaxies above the SFMS ($\Delta A_V \sim 0.07$ mag). The dependence of the offset on $\Delta$SFMS suggests that nebular attenuation on kpc scales is regulated not only by local star formation activity, but also by the global evolutionary state of the host galaxy. Together, these results indicate that the resolved $A_V$--$\Sigma_{\mathrm{SFR}}$ relation is not universal, and that locally calibrated attenuation relations may not fully describe galaxies at intermediate redshift. This highlights the need for attenuation calibrations that account for galaxy population and redshift when interpreting spatially resolved galaxy properties.

astro-ph.GA↗

arXiv2025

Transition of blue-core helicon discharge

This study explores the transitional characteristics of blue-core helicon discharge, which to our knowledge was not particularly focused on before. Parameters are measured on recently built advanced linear plasma device, i.e. Multiple Plasma Simulation Linear Device (MPS-LD) by various diagnostics including Langmuir probe, optical emission spectrometer, and standard high-speed camera. It is found that the jump direction of electron density (from low level to high level) is opposite to that of electron temperature (from high level to low level). Electron density increases significantly and the radial profile becomes localized near the axis when the blue-core transition occurs. With increased field strength, electron density increases whereas electron temperature drops. The radial profile of electron temperature looks like a ``W" shape, i.e. minimizing around the edge of blue-core column. Electron density increases with background pressure, while electron temperature peaks around certain pressure value. High-speed videos show that the plasma column oscillates radially and experiences azimuthal instabilities with high rate once entered blue-core mode. An electromagnetic solver (EMS) based on Maxwell's equations and a cold-plasma dielectric tensor is also employed to compute the wave field and power absorption during blue-core transition, to provide more details that are valuable for understanding the transitional physics but not yet available in experiment. The results show that wave field in both radial and axial directions changes significantly during the transition, its structure differs from antenna to downstream, and the power dependence of wave magnetic field is overall opposite to that of wave electric field. This work presents comprehensive characteristics of the transitional blue-core discharge and is important to both physics understanding and practical applications.

physics.plasm-ph↗

arXiv2024

Superconductivity Discovered in Niobium Polyhydride at High Pressures

Niobium polyhydride was synthesized at high pressure and high temperature conditions by using diamond anvil cell combined with in situ high pressure laser heating techniques. High pressure electric transport experiments demonstrate that superconducting transition occurs with critical temperature(Tc) 42 K at 187 GPa. The shift of Tc as function of external applied magnetic field is in consistent to the nature of superconductivity while the upper critical field at zero temperature Hc2(0) is estimated to~16.8 Tesla while the GL coherent length ~57 angstrom is estimated. The structure investigation using synchrotron radiation implies that the observed superconductivity may come from Fm-3m phase of NbH3.

cond-mat.supr-con↗

arXiv2023

The MAGPI Survey: Drivers of kinematic asymmetries in the ionised gas of $z\sim0.3$ star-forming galaxies

Galaxy gas kinematics are sensitive to the physical processes that contribute to a galaxy's evolution. It is expected that external processes will cause more significant kinematic disturbances in the outer regions, while internal processes will cause more disturbances for the inner regions. Using a subsample of 47 galaxies ($0.27<z<0.36$) from the Middle Ages Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey, we conduct a study into the source of kinematic disturbances by measuring the asymmetry present in the ionised gas line-of-sight velocity maps at the $0.5R_e$ (inner regions) and $1.5R_e$ (outer regions) elliptical annuli. By comparing the inner and outer kinematic asymmetries, we aim to better understand what physical processes are driving the asymmetries in galaxies. We find the local environment plays a role in kinematic disturbance, in agreement with other integral field spectroscopy studies of the local universe, with most asymmetric systems being in close proximity to a more massive neighbour. We do not find evidence suggesting that hosting an Active Galactic Nucleus (AGN) contributes to asymmetry within the inner regions, with some caveats due to emission line modelling. In contrast to previous studies, we do not find evidence that processes leading to asymmetry also enhance star formation in MAGPI galaxies. Finally, we find a weak anti-correlation between stellar mass and asymmetry (ie. high stellar mass galaxies are less asymmetric). We conclude by discussing possible sources driving the asymmetry in the ionised gas, such as disturbances being present in the colder gas phase (either molecular or atomic) prior to the gas being ionised, and non-axisymmetric features (e.g., a bar) being present in the galactic disk. Our results highlight the complex interplay between ionised gas kinematic disturbances and physical processes involved in galaxy evolution.

astro-ph.GA↗

arXiv2023

Superconductivity with Tc 116K discovered in antimony polyhydrides

Superconductivity (SC) was experimentally observed for the first time in antimony polyhydride. The diamond anvil cell combined with laser heating system was used to synthesize the antimony polyhydride sample at high pressure and high temperature conditions. In-situ high pressure transport measurements as function of temperature with applied magnet are performed to study the SC properties. It was found that the antimony polyhydride samples show superconducting transition with critical temperature Tc 116 K at 184 GPa. The investigation of SC at magnetic field revealed that the superconducting coherent length ~40 angstroms based on Ginzburg Landau (GL) equation. Antimony polyhydride superconductor has the second highest Tc in addition to sulfur hydride among the polyhydrides of elements from main group IIIA to VIIA in periodic table.

cond-mat.supr-con↗

arXiv2023

Field-free all-optical switching and electrical read-out of Tb/Co-based magnetic tunnel junctions

Switching of magnetic tunnel junction using femto-second laser enables a possible path for THz frequency memory operation, which means writing speeds 2 orders of magnitude faster than alternative electrical approaches based on spin transfer or spin orbit torque. In this work we demonstrate successful field-free 50fs single laser pulse driven magnetization reversal of [Tb/Co] based storage layer in a perpendicular magnetic tunnel junction. The nanofabricated magnetic tunnel junction devices have an optimized bottom reference electrode and show Tunnel Magnetoresistance Ratio values (TMR) up to 74\% after patterning down to sub-100nm lateral dimensions. Experiments on continuous films reveal peculiar reversal patterns of concentric rings with opposite magnetic directions, above certain threshold fluence. These rings have been correlated to patterned device switching probability as a function of the applied laser fluence. Moreover, the magnetization reversal is independent on the duration of the laser pulse. According to our macrospin model, the underlying magnetization reversal mechanism can be attributed to an in-plane reorientation of the magnetization due to a fast reduction of the out-of-plane uniaxial anisotropy. These aspects are of great interest both for the physical understanding of the switching phenomenon and their consequences for all-optical-switching memory devices, since they allow for a large fluence operation window with high resilience to pulse length variability.

physics.app-ph↗

arXiv2022

Superconductivity Observed in Tantalum Polyhydride at High Pressure

We report experimental discovery of tantalum polyhydride superconductor. It was synthesized at high pressure and high temperature conditions using diamond anvil cell combined with in-situ high pressure laser heating techniques. The superconductivity was investigated via resistance measurements at pressures. The highest superconducting transition temperature Tc was found to be ~30 K at 197 GPa in the sample that was synthesized at the same pressure with ~2000 K heating. The transitions are shifted to low temperature upon applying magnetic fields that supports the superconductivity nature. The upper critical field at zero temperature {\mu}0Hc2(0) of the superconducting phase is estimated to be ~20 T that corresponds to GL coherent length ~40 angstroms. Our results suggest that the superconductivity may arise from I-43d phase of TaH3. It is, for the first time to our best knowledge, experimental realization of superconducting hydrides for the VB group of transitional metals.

cond-mat.supr-con↗

arXiv2022

In plane reorientation induced single laser pulse magnetization reversal in rare-earth based multilayer

Single Pulse All Optical Helicity Independent Switching (AO-HIS) represents the ability to reverse the magnetic moment of a nanostructure using a femtosecond single laser pulse. It is an ultrafast method to manipulate magnetization without the use of any applied field. Since the first switching experiments carried on GdFeCo ferrimagnetic systems, single pulse AO-HIS has been restricted for a while to Gd-based alloys or Gd/FM bilayers where FM is a ferromagnetic layer. Only recently has AO-HIS been extended to a few other materials: MnRuGa ferrimagnetic Heusler alloys and Tb/Co multilayers with a very specific range of thickness and composition. Here, we demonstrate that single pulse AO-HIS observed in Tb/Co results from a different mechanism than the one for Gd based samples and that it can be obtained for a large range of rare earth-transition metal (RE-TM) multilayers, making this phenomenon much more general. Surprisingly, in this large family of (RE-TM) multilayer systems, the threshold fluence for switching is observed to be independent of the pulse duration, up to at least 12 ps. Moreover, at high laser intensities, concentric ring domain structures are induced, unveiling multiple fluence thresholds. These striking switching features, which are in contrast to those of AO-HIS in GdFeCo alloys, concomitant with the demonstration of an in-plane reorientation of the magnetization, point towards an intrinsic precessional reversal mechanism. Our results allow expanding the variety of materials with tunable magnetic properties that can be integrated in complex heterostructures and provide a pathway to engineer materials for future applications based on all-optical control of magnetic order.

cond-mat.mtrl-sci↗

arXiv2022

COSMOS2020: The Galaxy Stellar Mass Function: the assembly and star formation cessation of galaxies at $0.2\lt z \leq 7.5$

How galaxies form, assemble, and cease their star-formation is a central question within the modern landscape of galaxy evolution studies. These processes are indelibly imprinted on the galaxy stellar mass function (SMF). We present constraints on the shape and evolution of the SMF, the quiescent galaxy fraction, and the cosmic stellar mass density across 90% of the history of the Universe from $z=7.5\rightarrow0.2$ via the COSMOS survey. Now with deeper and more homogeneous near-infrared coverage exploited by the COSMOS2020 catalog, we leverage the large 1.27 deg$^{2}$ effective area to improve sample statistics and understand cosmic variance particularly for rare, massive galaxies and push to higher redshifts with greater confidence and mass completeness than previous studies. We divide the total stellar mass function into star-forming and quiescent sub-samples through $NUVrJ$ color-color selection. Measurements are then fitted with Schechter functions to infer the intrinsic SMF, the evolution of its key parameters, and the cosmic stellar mass density out to $z=7.5$. We find a smooth, monotonic evolution in the galaxy SMF since $z=7.5$, in agreement with previous studies. The number density of star-forming systems seems to have undergone remarkably consistent growth spanning four decades in stellar mass from $z=7.5\rightarrow2$ whereupon high-mass systems become predominantly quiescent (i.e. downsizing). An excess of massive systems at $z\sim2.5-5.5$ with strikingly red colors, some newly identified, increase the observed number densities to the point where the SMF cannot be reconciled with a Schechter function. Systematics including cosmic variance and/or AGN contamination are unlikely to fully explain this excess, and so we speculate that there may be contributions from dust-obscured objects similar to those found in FIR surveys. (abridged)

astro-ph.GA↗

arXiv2022

Superconductivity above 80 K in polyhydrides of hafnium

Studies on polyhydrides are attracting growing attentions recently due to their potential high temperature superconductivity (SC). We here report the discovery of SC in hafnium polyhydrides at high pressures. The hafnium superhydrides are synthesized at high pressure and high temperature conditions using diamond anvil cell in combination with in-situ high pressure laser heating technique. The SC was investigated by in-situ high pressure resistance measurements in applied magnetic fields. A superconducting transition with onset Tc ~83 K was observed at 243 GPa. The upper critical field Hc2(0) was estimated to be 24 Tesla by GL theory and the consequent superconducting coherent length to be ~37 angstrom. Our results suggest that the superconducting phase is from C2/m-HfH14. This is the first 5d transition metal polyhydride superconductor with Tc above the liquid nitrogen temperature.

cond-mat.supr-con↗

arXiv2022

Snowmass 2021 White Paper on Upgrading SuperKEKB with a Polarized Electron Beam: Discovery Potential and Proposed Implementation

Upgrading the SuperKEKB electron-positron collider with polarized electron beams opens a new program of precision physics at a center-of-mass energy of 10.58 GeV. This white paper describes the physics potential of this `Chiral Belle' program. It includes projections for precision measurements of $\sin^2\theta_W$ that can be obtained from independent left-right asymmetry measurements of $e^+e^-$ transitions to pairs of electrons, muons, taus, charm and b-quarks. The $\sin^2\theta_W$ precision obtainable at SuperKEKB will match that of the LEP/SLC world average, but at the centre-of-mass energy of 10.58 GeV. Measurements of the couplings for muons, charm, and $b$-quarks will be substantially improved and the existing $3\sigma$ discrepancy between the SLC $A_{LR}$ and LEP $A_{FB}^b$ measurements will be addressed. Precision measurements of neutral current universality will be more than an order of magnitude more precise than currently available. As the energy scale is well away from the $Z^0$-pole, the precision measurements will have sensitivity to the presence of a parity-violating dark sector gauge boson, $Z_{\rm dark}$. The program also enables the measurement of the anomalous magnetic moment $g-2$ form factor of the $\tau$ to be made at an unprecedented level of precision. A precision of $10^{-5}$ level is accessible with 40~ab$^{-1}$ and with more data it would start to approach the $10^{-6}$ level. This technique would provide the most precise information from the third generation about potential new physics explanations of the muon $g-2$ $4\sigma$ anomaly. Additional $\tau$ and QCD physics programs enabled or enhanced with having polarized electron beams are also discussed in this White Paper. This paper includes a summary of the path forward in R&D and next steps required to implement this upgrade and access its exciting discovery potential.

physics.acc-ph↗

arXiv2021

Record High Tc Element Superconductivity Achieved In Titanium

It is challenging to search for high Tc superconductivity (SC) in transition metal elements wherein d electrons are usually not favored by conventional BCS theory. Here we report discovery of surprising SC up to 310 GPa with Tc above 20 K in wide pressure range from 108 GPa to 240 GPa in titanium. The maximum Tc^onset above 26 K and zero resistance Tc^zero of 21 K are record high values hitherto achieved among element superconductors. The Hc2(0) is estimated to be about 32 Tesla with coherence length 32 angstrom. The results show strong s-d transfer and d-band dominance, indicating correlation driven contributions to high Tc SC in dense titanium. This finding is in sharp contrast to the theoretical predications based on pristine electron-phonon coupling scenario. The study opens a fresh promising avenue for rational design and discovery of high Tc superconductors among simple materials via pressure tuned unconventional mechanism.

cond-mat.supr-con↗

arXiv2021

Long-lived Andreev states as evidence for protected hinge modes in a bismuth nanoring Josephson junction

Second-order topological insulators are characterized by helical, non-spin-degenerate, one-dimensional states running along opposite crystal hinges, with no backscattering. Injecting superconducting pairs therefore entails splitting Cooper pairs into two families of helical Andreev states of opposite helicity, one at each hinge. Here we provide evidence for such separation via the measurement and analysis of switching supercurrent statistics of a crystalline nanoring of bismuth. Using a phenomenological model of two helical Andreev hinge modes, we find that pairs relax at a rate comparable to individual quasiparticles, in contrast with the much faster pair relaxation of non-topological systems. This constitutes a unique tell-tale sign of the spatial separation of topological helical hinges.

cond-mat.mes-hall↗

arXiv2021

COSMOS2020: A panchromatic view of the Universe to $z\sim10$ from two complementary catalogs

The Cosmic Evolution Survey (COSMOS) has become a cornerstone of extragalactic astronomy. Since the last public catalog in 2015, a wealth of new imaging and spectroscopic data has been collected in the COSMOS field. This paper describes the collection, processing, and analysis of this new imaging data to produce a new reference photometric redshift catalog. Source detection and multi-wavelength photometry is performed for 1.7 million sources across the $2\,\mathrm{deg}^{2}$ of the COSMOS field, $\sim$966,000 of which are measured with all available broad-band data using both traditional aperture photometric methods and a new profile-fitting photometric extraction tool, The Farmer, which we have developed. A detailed comparison of the two resulting photometric catalogs is presented. Photometric redshifts are computed for all sources in each catalog utilizing two independent photometric redshift codes. Finally, a comparison is made between the performance of the photometric methodologies and of the redshift codes to demonstrate an exceptional degree of self-consistency in the resulting photometric redshifts. The $i<21$ sources have sub-percent photometric redshift accuracy and even the faintest sources at $25<i<27$ reach a precision of $5\,\%$. Finally, these results are discussed in the context of previous, current, and future surveys in the COSMOS field. Compared to COSMOS2015, reaches the same photometric redshift precision at almost one magnitude deeper. Both photometric catalogs and their photometric redshift solutions and physical parameters will be made available through the usual astronomical archive systems (ESO Phase 3, IPAC IRSA, and CDS).

astro-ph.GA↗

arXiv2020

The MAGPI Survey -- science goals, design, observing strategy, early results and theoretical framework

We present an overview of the Middle Ages Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey, a Large Program on ESO/VLT. MAGPI is designed to study the physical drivers of galaxy transformation at a lookback time of 3-4 Gyr, during which the dynamical, morphological, and chemical properties of galaxies are predicted to evolve significantly. The survey uses new medium-deep adaptive optics aided MUSE observations of fields selected from the GAMA survey, providing a wealth of publicly available ancillary multi-wavelength data. With these data, MAGPI will map the kinematic and chemical properties of stars and ionised gas for a sample of 60 massive (> 7 x 10^10 M_Sun) central galaxies at 0.25 < z <0.35 in a representative range of environments (isolated, groups and clusters). The spatial resolution delivered by MUSE with Ground Layer Adaptive Optics (GLAO, 0.6-0.8 arcsec FWHM) will facilitate a direct comparison with Integral Field Spectroscopy surveys of the nearby Universe, such as SAMI and MaNGA, and at higher redshifts using adaptive optics, e.g. SINS. In addition to the primary (central) galaxy sample, MAGPI will deliver resolved and unresolved spectra for as many as 150 satellite galaxies at 0.25 < z <0.35, as well as hundreds of emission-line sources at z < 6. This paper outlines the science goals, survey design, and observing strategy of MAGPI. We also present a first look at the MAGPI data, and the theoretical framework to which MAGPI data will be compared using the current generation of cosmological hydrodynamical simulations including EAGLE, Magneticum, HORIZON-AGN, and Illustris-TNG. Our results show that cosmological hydrodynamical simulations make discrepant predictions in the spatially resolved properties of galaxies at z ~ 0.3. MAGPI observations will place new constraints and allow for tangible improvements in galaxy formation theory.

astro-ph.GA↗

arXiv2020

MOONRISE: The Main MOONS GTO Extragalactic Survey

The MOONS instrument possesses an exceptional combination of large multiplexing, high sensitivity, broad simultaneous spectral coverage (from optical to near-infrared bands), large patrol area and high fibre density. These properties provide the unprecedented potential of enabling, for the very first time, SDSS-like surveys around Cosmic Noon (z~1-2.5), when the star formation rate in the Universe peaked. The high-quality spectra delivered by MOONS will sample the same nebular and stellar diagnostics observed in extensive surveys of local galaxies, providing an accurate and consistent description of the evolution of various physical properties of galaxies, and hence a solid test of different scenarios of galaxy formation and transformation. Most importantly, by spectroscopically identifying hundreds of thousands of galaxies at high redshift, the MOONS surveys will be capable of determining the environments in which primeval galaxies lived and will reveal how such environments affected galaxy evolution. In this article, we specifically focus on the main Guaranteed Time Observation (GTO) MOONS extragalactic survey, MOONRISE, by providing an overview of its scientific goals and observing strategy.

astro-ph.GA↗

arXiv2020

S2COSMOS: Evolution of Gas Mass with Redshift Using Dust Emission

We investigate the evolution of the gas mass fraction for galaxies in the COSMOS field using submillimetre emission from dust at 850$\mu$m. We use stacking methodologies on the 850$\mu$m S2COSMOS map to derive the gas mass fraction of galaxies out to high redshifts, 0 <= $z$ <= 5, for galaxies with stellar masses of $10^{9.5} < M_* (\rm M_{\odot}) < 10^{11.75}$. In comparison to previous literature studies we extend to higher redshifts, include more normal star-forming galaxies (on the main sequence), and also investigate the evolution of the gas mass fraction split by star-forming and passive galaxy populations. We find our stacking results broadly agree with scaling relations in the literature. We find tentative evidence for a peak in the gas mass fraction of galaxies at around $z$ ~ 2.5-3, just before the peak of the star formation history of the Universe. We find that passive galaxies are particularly devoid of gas, compared to the star-forming population. We find that even at high redshifts, high stellar mass galaxies still contain significant amounts of gas.

astro-ph.GA↗