arXiv subjects

J. Yang

Publications and source records attributed to J. Yang.

At least 91 records · Page 5Linked to original sources

arXiv2022

Spin-Triplet Superconductivity in K2Cr3As3

A spin-triplet superconductor can harbor Majorana bound states that can be used in topological quantum computing. Recently, K2Cr3As3 and its variants with critical temperature Tc as high as 8 K have emerged as a new class of superconductors with ferromagnetic spin fluctuations. Here we report a discovery in K2Cr3As3 single crystal that, the spin susceptibility measured by 75As Knight shift below Tc is unchanged with the magnetic field H0 applied in the ab plane, but vanishes toward zero temperature when H0 is along the c axis, which unambiguously establishes this compound as a spin-triplet superconductor described by a vector order-parameter d parallel to the c axis. Combining with points-nodal gap we show that K2Cr3As3 is a new platform for the study of topological superconductivity and its possible technical application.

cond-mat.supr-con↗

arXiv2021

Search for "Invisible" Axion Dark Matter in the $3.3\text{-}4.2~μ$eV Mass Range

We report the results from a haloscope search for axion dark matter in the $3.3\text{-}4.2~μ$eV mass range. This search excludes the axion-photon coupling predicted by one of the benchmark models of "invisible" axion dark matter, the KSVZ model. This sensitivity is achieved using a large-volume cavity, a superconducting magnet, an ultra low noise Josephson parametric amplifier, and sub-Kelvin temperatures. The validity of our detection procedure is ensured by injecting and detecting blind synthetic axion signals.

hep-ex↗

arXiv2021

Anomalous Magnetoresistance by Breaking Ice Rule in Bi2Ir2O7/Dy2Ti2O7 Heterostructure

While geometrically frustrated quantum magnets are known for a variety of exotic spin states that are of great interests of understanding emergent phenomena as well as enabling revolutionary quantum technologies, most of them are necessarily good insulators which are difficult to be integrated with modern electrical circuit that relies on moving charge carriers. The grand challenge of converting fluctuations and excitations of frustrated moments into electronic responses is finding ways to introduce charge carriers that interact with the localized spins without destroying the spin states. Here, we show that, by designing a Bi2Ir2O7/Dy2Ti2O7 heterostructure, the breaking of the spin ice rule in insulating Dy2Ti2O7 can lead to a charge response in the Bi2Ir2O7 conducting layer that can be detected as anomalous magnetoresistance. These results demonstrate a novel and feasible interfacial approach for electronically probing exotic spin states in insulating magnets, laying out a blueprint for the metallization of frustrated quantum magnets.

cond-mat.str-el↗

arXiv2021

Local mechanism of valence bond formation in IrTe$_2$

Doped IrTe$_2$ is considered a platform for topological superconductivity and therefore receives currently a lot of interest. In addition, the superconductivity in these materials exists in close vicinity of electronic valence bond crystals, which we explore here by means of high-pressure single crystal x-ray diffraction in combination with density functional theory. Our crystallographic refinements provide unprecedented information about the structural evolution as a function of applied pressure up to 42 GPa. Using this structural information for density functional theory calculations, we show that the valence bond formation in IrTe$_2$ is driven by changes in the Ir-Te-Ir bond angle. When a valence bond is formed, this bond angle decreases drastically, leading to a stabilization of local valence bonds large enough to push them out of a broad band continuum. This unusual local mechanism of valence bond formation in an itinerant material provides a natural explanation for the different valence bond orders in IrTe$_2$, implies a very strong electron-phonon coupling and is most likely relevant for the superconductivity as well.

cond-mat.str-el↗

arXiv2021

Milliarcsecond localisation of the repeating FRB 20201124A

Very long baseline interferometric (VLBI) localisations of repeating fast radio bursts (FRBs) have demonstrated a diversity of local environments: from nearby star-forming regions to globular clusters. Here we report the VLBI localisation of FRB 20201124A using an ad-hoc array of dishes that also participate in the European VLBI Network (EVN). In our campaign, we detected 18 total bursts from FRB 20201124A at two separate epochs. By combining the visibilities from both observing epochs, we were able to localise FRB 20201124A with a 1-$σ$ error of 4.5 milliarcseconds (mas). We use the relatively large burst sample to investigate astrometric accuracy, and find that for $\gtrsim20$ baselines ($\gtrsim7$ dishes) that we can robustly reach milliarcsecond precision even using single-burst data sets. Sub-arcsecond precision is still possible for single bursts, even when only $\sim$ six baselines (four dishes) are available. We explore two methods for determining the individual burst positions: the peaks of the dirty maps and a Gaussian fit to the cross fringe pattern on the dirty maps. We found the latter to be more reliable due to the lower mean and standard deviation in the offsets from the FRB position. Our VLBI work places FRB 20201124A 705$\pm$26 mas (1-$σ$ errors) from the optical centre of the host galaxy, and consistent with originating from within the recently-discovered extended radio structure associated with star-formation in the host galaxy. Future high-resolution optical observations, e.g. with Hubble Space Telescope, can determine the proximity of our FRB 20201124A VLBI position to nearby knots of star formation.

astro-ph.HE↗

arXiv2021

Single laser pulse driven thermal limit of the quasi-two dimensional magnetic ordering in Sr$_2$IrO$_4$

Upon femtosecond-laser stimulation, generally materials are expected to recover back to their thermal-equilibrium conditions, with only a few exceptions reported. Here we demonstrate that deviation from the thermal-equilibrium pathway can be induced in canonical 3D antiferromagnetically (AFM) ordered Sr$_2$IrO$_4$ by a single 100-fs-laser pulse, appearing as losing long-range magnetic correlation along one direction into a glassy condition. We further discover a `critical-threshold ordering' behavior for fluence above approximately 12 mJ/cm$^2$ which we show corresponds to the smallest thermodynamically stable $c$-axis correlation length needed to maintain long-range quasi-two-dimensional AFM order. We suggest that this behavior arises from the crystalline anisotropy of the magnetic-exchange parameters in Sr$_2$IrO$_4$, whose strengths are associated with distinctly different timescales. As a result, they play out very differently in the ultrafast recovery processes, compared with the thermal equilibrium evolution. Thus, our observations are expected to be relevant to a wide range of problems in the nonequilibrium behavior of low-dimensional magnets and other related ordering phenomena.

cond-mat.str-el↗

arXiv2021

Dark Matter Axion Search Using a Josephson Traveling Wave Parametric Amplifier

We present a new exclusion bound of axion-like particle dark matter with axion-photon couplings above $\mathrm{10^{-13}}$ $\mathrm{GeV^{-1}}$ over the frequency range 4796.7--4799.5 MHz, corresponding to a narrow range of axion masses centered around 19.84 $μ$eV. This measurement represents the first implementation of a Josephson Traveling Wave Parametric Amplifier (JTWPA) in a dark matter search. The JTWPA was operated in the insert of the Axion Dark Matter eXperiment (ADMX) as part of an independent receiver chain that was attached to a 0.588-liter cavity. The ability of the JTWPA to deliver high gain over a wide (3 GHz) bandwidth has engendered interest from those aiming to perform broadband axion searches, a longstanding goal in this field.

hep-ex↗

arXiv2021

Burst timescales and luminosities link young pulsars and fast radio bursts

Fast radio bursts (FRBs) are extragalactic radio flashes of unknown physical origin. Their high luminosities and short durations require extreme energy densities, like those found in the vicinity of neutron stars and black holes. Studying the burst intensities and polarimetric properties on a wide range of timescales, from milliseconds down to nanoseconds, is key to understanding the emission mechanism. However, high-time-resolution studies of FRBs are limited by their unpredictable activity levels, available instrumentation and temporal broadening in the intervening ionised medium. Here we show that the repeating FRB 20200120E can produce isolated shots of emission as short as about 60 nanoseconds in duration, with brightness temperatures as high as $3\times 10^{41}$ K (excluding relativistic effects), comparable to `nano-shots' from the Crab pulsar. Comparing both the range of timescales and luminosities, we find that FRB 20200120E observationally bridges the gap between known Galactic young pulsars and magnetars, and the much more distant extragalactic FRBs. This suggests a common magnetically powered emission mechanism spanning many orders of magnitude in timescale and luminosity. In this work, we probe a relatively unexplored region of the short-duration transient phase space; we highlight that there likely exists a population of ultra-fast radio transients at nanosecond to microsecond timescales, which current FRB searches are insensitive to.

astro-ph.HE↗

arXiv2021

A repeating fast radio burst source in a globular cluster

Fast radio bursts (FRBs) are exceptionally luminous flashes of unknown physical origin, reaching us from other galaxies (Petroff et al. 2019). Most FRBs have only ever been seen once, while others flash repeatedly, though sporadically (Spitler et al. 2016, CHIME/FRB Collaboration et al. 2021). Many models invoke magnetically powered neutron stars (magnetars) as the engines producing FRB emission (Margalit & Metzger 2018, CHIME/FRB Collaboration et al. 2020). Recently, CHIME/FRB announced the discovery (Bhardwaj et al. 2021) of the repeating FRB 20200120E, coming from the direction of the nearby grand design spiral galaxy M81. Four potential counterparts at other observing wavelengths were identified (Bhardwaj et al. 2021) but no definitive association with these sources, or M81, could be made. Here we report an extremely precise localisation of FRB 20200120E, which allows us to associate it with a globular cluster (GC) in the M81 galactic system and to place it ~2pc offset from the optical center of light of the GC. This confirms (Bhardwaj et al. 2021) that FRB 20200120E is 40 times closer than any other known extragalactic FRB. Because such GCs host old stellar populations, this association strongly challenges FRB models that invoke young magnetars formed in a core-collapse supernova as powering FRB emission. We propose, instead, that FRB 20200120E is a highly magnetised neutron star formed via either accretion-induced collapse of a white dwarf or via merger of compact stars in a binary system (Margalit et al. 2019). Alternative scenarios involving compact binary systems, efficiently formed inside globular clusters, could also be responsible for the observed bursts.

astro-ph.HE↗

arXiv2021

$E_8$ Spectra of Quasi-one-dimensional Antiferromagnet BaCo$_2$V$_2$O$_8$ under Transverse Field

We report $^{51}$V nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) measurements on a quasi-1D antiferromagnet BaCo$_2$V$_2$O$_8$ under transverse field along the [010] direction. The scaling behavior of the spin-lattice relaxation rate above the Néel temperatures unveils a 1D quantum critical point (QCP) at $H_c^{1D}\approx 4.7$ T, which is masked by the 3D magnetic order. With the aid of accurate analytical analysis and numerical calculations, we show that the zone center INS spectrum at $H_c^{1D}$ is precisely described by the pattern of the 1D quantum Ising model in a magnetic field, a class of universality described in terms of the exceptional $E_8$ Lie algebra. These excitations keep to be non-diffusive over a certain field range when the system is away from the 1D QCP. Our results provide an unambiguous experimental realization of the massive $E_8$ phase in the compound, and open new experimental route for exploring the dynamics of quantum integrable systems as well as physics beyond integrability.

cond-mat.str-el↗

arXiv2021

Conformer-specific Chemistry Imaged in Real Space and Time

Conformational isomers or conformers of molecules play a decisive role in chemistry and biology. However, experimental methods to investigate chemical reaction dynamics are typically not conformer-sensitive. Here, we report on a gas-phase megaelectronvolt ultrafast electron diffraction investigation of α-phellandrene undergoing an electrocyclic ring-opening reaction. We directly image the evolution of a specific set of α-phellandrene conformers into the product isomer predicted by the Woodward-Hoffmann rules in real space and time. Our experimental results are in quantitative agreement with nonadiabatic quantum molecular dynamics simulations, which provide unprecedented detail of how conformation influences time scale and quantum efficiency of photoinduced ring-opening reactions. Due to the prevalence of large numbers of conformers in organic chemistry, our findings impact our general understanding of reaction dynamics in chemistry and biology.

physics.chem-ph↗

arXiv2021

The filamentary structures in the CO emission toward the Milky Way disk

We present a statistical study of the filamentary structure orientation in the CO emission observations obtained in the Milky Way Imaging Scroll Painting (MWISP) survey in the range $25.8°< l < 49.7°$, $|b| \leq 1.25°$, and $-100 < v_{\rm LSR} < 135$ km/s. We found that most of the filamentary structures in the $^{12}$CO and $^{13}$CO emission do not show a global preferential orientation either parallel or perpendicular to the Galactic plane. However, we found ranges in Galactic longitude and radial velocity where the $^{12}$CO and $^{13}$CO filamentary structures are parallel to the Galactic plane. These preferential orientations are different from those found for the HI emission. We consider this an indication that the molecular structures do not simply inherit these properties from parental atomic clouds. Instead, they are shaped by local physical conditions, such as stellar feedback, magnetic fields, and Galactic spiral shocks.

astro-ph.GA↗

arXiv2021

Hourly Warning for Strong Earthquakes

A promising perspective is presented that humans can provide hourly warning for strong land earthquakes (EQs, Ms6). Two important atmospheric electrostatic signal features are described. A table that lists 9 strong land EQs with shock time, epicenter, magnitude, weather in the region near the epicenter, precursor beginning time, and precursor duration demonstrates that at approximately several hours to one day before a strong land EQ, the weather conditions are fair near the epicenter, and an abnormal negative atmospheric electrostatic signal is very obvious. Moreover, the mechanism is explained. A method by which someone could determine the epicenter and the magnitude of a forthcoming strong EQ is suggested. Finally, the possibility of realizing hourly warning for strong land EQs in the near future is pointed out.

physics.geo-ph↗

arXiv2021

An ALMA multi-line survey of the ISM in two quasar host-companion galaxy pairs at $z > 6$

We present a multi-line survey of the interstellar medium (ISM) in two $z>6$ quasar (QSO) host galaxies, PJ231-20 ($z=6.59$) and PJ308-21 ($z=6.23$), and their two companion galaxies. Observations were carried out using the Atacama Large (sub-)Millimeter Array (ALMA). We targeted eleven transitions including atomic fine structure lines (FSLs) and molecular lines: [NII]$_{\rm 205μm}$, [CI]$_{\rm 369μm}$, CO ($J_{\rm up} = 7, 10, 15, 16$), H$_2$O $3_{12}-2_{21}$, $3_{21}-3_{12}$, $3_{03}-2_{12}$, and the OH$_{\rm 163μm}$ doublet. The underlying far-infrared (FIR) continuum samples the Rayleigh-Jeans tail of the respective dust emission. By combining this information with our earlier ALMA [CII]$_{\rm 158μm}$ observations, we explore the effects of star formation and black hole feedback on the galaxies' ISM using the CLOUDY radiative transfer models. We estimate dust masses, spectral indexes, IR luminosities, and star-formation rates from the FIR continuum. The analysis of the FSLs indicates that the [CII]$_{\rm 158μm}$ and [CI]$_{\rm 369μm}$ emission arises predominantly from the neutral medium in photodissociation regions (PDRs). We find that line deficits are in agreement with those of local luminous infrared galaxies. The CO spectral line energy distributions (SLEDs), reveal significant high-$J$ CO excitation in both quasar hosts. Our CO SLED modeling of the quasar PJ231-20 shows that PDRs dominate the molecular mass and CO luminosities for $J_{\rm up}\le 7$, while the $J_{\rm up}\ge10$ CO emission is likely driven by X-ray dissociation regions produced by the active galactic nucleus (AGN) at the very center of the quasar host [abridged].

astro-ph.GA↗

arXiv2021

Laser-Induced Transient Magnons in Sr3Ir2O7 Throughout the Brillouin Zone

Although ultrafast manipulation of magnetism holds great promise for new physical phenomena and applications, targeting specific states is held back by our limited understanding of how magnetic correlations evolve on ultrafast timescales. Using ultrafast resonant inelastic x-ray scattering we demonstrate that femtosecond laser pulses can excite transient magnons at large wavevectors in gapped antiferromagnets, and that they persist for several picoseconds which is opposite to what is observed in nearly gapless magnets. Our work suggests that materials with isotropic magnetic interactions are preferred to achieve rapid manipulation of magnetism.

cond-mat.str-el↗

arXiv2021

A Peculiarly Short-duration Gamma-Ray Burst from Massive Star Core Collapse

Gamma-ray bursts (GRBs) have been phenomenologically classified into long and short populations based on the observed bimodal distribution of duration. Multi-wavelength and multi-messenger observations in recent years have revealed that in general long GRBs originate from massive star core collapse events, whereas short GRBs originate from binary neutron star mergers. It has been known that the duration criterion is sometimes unreliable, and multi-wavelength criteria are needed to identify the physical origin of a particular GRB. Some apparently long GRBs have been suggested to have a neutron star merger origin, whereas some apparently short GRBs have been attributed to genuinely long GRBs whose short, bright emission is slightly above the detector's sensitivity threshold. Here we report the comprehensive analysis of the multi-wavelength data of a bright short GRB 200826A. Characterized by a sharp pulse, this burst shows a duration of 1 second and no evidence of an underlying longer-duration event. Its other observational properties such as its spectral behaviors, total energy, and host galaxy offset, are, however, inconsistent with those of other short GRBs believed to originate from binary neutron star mergers. Rather, these properties resemble those of long GRBs. This burst confirms the existence of short duration GRBs with stellar core-collapse origin, and presents some challenges to the existing models.

astro-ph.HE↗

arXiv2021

Effect of lattice excitations on transient near edge X-ray absorption spectroscopy

Time-dependent and constituent-specific spectral changes in soft near edge X-ray spectroscopy (XAS) of an [Fe/MgO]$_8$ metal/insulator heterostructure upon laser excitation are analyzed at the O K-edge with picosecond time resolution. The oxygen absorption edge of the insulator features a uniform intensity decrease of the fine structure at elevated phononic temperatures, which can be quantified by a simple simulation and fitting procedure presented here. Combining X-ray absorption spectroscopy with ultrafast electron diffraction measurements and ab initio calculations demonstrate that the transient intensity changes in XAS can be assigned to a transient lattice temperature. Thus, the sensitivity of transient near edge XAS to phonons is demonstrated.

cond-mat.mtrl-sci↗

arXiv2021

The jet collimation profile at high resolution in BL Lacertae

Controversial studies on the jet collimation profile of BL Lacertae (BL Lac), the eponymous blazar of BL Lac objects class, complicate the scenario in this already puzzling class of objects. Understanding the jet geometry, in connection with the jet kinematics and the physical conditions in the surrounding medium, is fundamental to better constrain the formation, acceleration and collimation mechanisms in extragalactic jets. With the aim of investigating the jet geometry in the innermost regions of the jet of BL Lac, and solving the controversy, we explore the radio jet in this source, using high resolution millimeter-wave VLBI data. We collect 86GHz GMVA and 43GHz VLBA data to obtain stacked images that we use to infer the jet collimation profile by means of two comparable methods. We analyze the kinematics at 86GHz, and we discuss it in the context of the jet expansion. Finally we consider a possible implication of the Bondi sphere in shaping the different expanding region observed along the jet. We found that the jet in BL Lac expands with an overall conical geometry. A higher expanding rate region is observed between ~5 and 10 pc (de-projected) from the black hole. Such a region is associated with the decrease in brightness usually observed in high-frequency VLBI images of BL Lac. The jet retrieves the original jet expansion around 17 pc, where the presence of a recollimation shock is supported by both the jet profile and the 15GHz kinematics (MOJAVE survey). The change in the jet expansion profile occurring at ~5 pc could be associated with a change in the external pressure profile in correspondence of the Bondi radius (~3.3X10$^5$$R_s$).

astro-ph.HE↗