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Solar prominences are very spectacular structures embedded in the tenuous and hot solar corona. The counterstreaming flows, a common feature in solar quiescent prominences, have been discovered for more than twenty years. However, the mechanism driving the counterstreaming flows is still elusive. To unveil the nature of this phenomenon, we analyzed the data of a quiescent prominence observed by the New Vacuum Solar Telescope (NVST), the Interface Region Imaging Spectrograph (IRIS), and the Solar Dynamical Observatory (SDO). It is found that there is a distinct longitudinal oscillation of prominence plasma along the higher part of the prominence spine in H$\alpha$ observations. The oscillation period is approximately 83 minutes and the amplitude is about 32 Mm. The counterstreaming flows are dominant in the middle part of the prominence spine. The velocities of the counterstreaming flows range from about 4 km s$^{-1}$ to 11 km s$^{-1}$. Moreover, the intermittent mass flows with the upward plumes from the top of the bubbles and tornado-like barbs are observed to be injected into the lower part of the prominence spine from the lower atmosphere. The velocities of these injected mass flows range from about 3 km s$^{-1}$ to 30 km s$^{-1}$. Some injected mass flows exhibit redshifted Doppler signals, while others exhibit blueshifted signals. Based on these high resolution observations, it is found that different parts of the prominence spine exhibit the different dynamic characteristics. These results further advance the understanding of the ubiquitous counterstreaming flows in solar quiescent prominences., Comment: 14 pages, 7 figures, accepted for publication in ApJ

Solar filaments are spectacular objects in the solar atmosphere, consisting of accumulations of cool, dense, and partially ionized plasma suspended in the hot solar corona against gravity. The magnetic structures that support the filament material remain elusive, partly due to the lack of high resolution magnetic field measurements in the chromosphere and corona. In this study, we reconstruct the magnetic structures of a solar intermediate filament using EUV observations and two different methods, to follow the injection of hot material from a B-class solar flare. Our analysis reveals the fine-scale magnetic structures of the filament, including a compact set of mutually wrapped magnetic fields encasing the cool filament material, two groups of helical magnetic structures intertwining with the main filament, and a series of arched magnetic loops positioned along the filament. Additionally, we also find that the northern footpoints of the helical structures are rooted in the same location, while their southern footpoints are rooted in different areas. The results obtained in this study offer new insights into the formation and eruption mechanisms of solar filaments., Comment: 23 pages, 13 figures, accepted for publication in ApJ

Antiferromagnetic (AFM) magnons in van der Waals (vdW) materials offer substantial potential for applications in magnonics and spintronics. In this study, we demonstrate ultra-strong magnon-magnon coupling in the GHz regime within a vdW AFM, achieving a maximum coupling rate of 0.91. Our investigation shows the tunability of coupling strength through temperature-dependent magnetic anisotropies. We compare coupling strength values derived from the gap size from the measured spectrum with those calculated directly through the coupling parameter and show that the gap size as a measure of coupling strength is limited for the ultra-strong coupling regime. Additionally, analytical calculations show the possibility to reach the deep-strong coupling regime by engineering the magnetic anisotropy. These findings highlight the potential of vdW AFMs as a model case to study magnetisation dynamics in low-symmetry magnetic materials.

Tuning magnetic properties in layered van der Waals (vdW) materials has captured a significant attention due to the efficient control of ground-states by heterostructuring and external stimuli. Electron doping by electrostatic gating, interfacial charge transfer and intercalation is particularly effective in manipulating the exchange and spin-orbit properties, resulting in a control of Curie temperature ($T_{\text{C}}$) and magnetic anisotropy. Here, we discover an uncharted role of intercalation to generate magnetic frustration. As a model study, we intercalate Na atoms into the vdW gaps of pristine Cr$_2$Ge$_2$Te$_6$ (CGT) where generated magnetic frustration leads to emerging spin-glass states coexisting with a ferromagnetic order. A series of dynamic magnetic susceptibility measurements/analysis confirms the formation of magnetic clusters representing slow dynamics with a distribution of relaxation times. The intercalation also modifies other macroscopic physical parameters including the significant enhancement of $T_{\text{C}}$ from 66\,K to 240\,K and the switching of magnetic easy-hard axis direction. Our study identifies intercalation as a unique route to generate emerging frustrated spin states in simple vdW crystals., Comment: 31 pages, 18 figures

The axion is well motivated in physics. It solves the strong charge conjugation-parity reversal problem CP in fundamental physics and the dark matter problem in astronomy. Its interaction with the electromagnetic field has been expected but never detected experimentally. Such particles may convert to radio waves in the environment with a strong magnetic field. Inspired by the idea, various research groups have been working on theoretical modeling and radio data analysis to search for the signature of radio signals generated by the axion conversion in the magnetosphere of compact stars, where the surface magnetic field as strong as $10^{13}$-$10^{14}$ G is expected. In this work, we calculate the observational properties of the axion-induced radio signals (AIRSs) in the neutron star magnetosphere, where both the total intensity and polarization properties of radio emission are derived. Based on the ray tracing method, assuming 100% linear polarization of radio waves generated in each conversion, we compute the polarization emission profile concerning different viewing angles. We note that plasma and general relativistic effects are important for the polarization properties of AIRSs. Our work suggests that AIRSs can be identified by the narrow bandwidth and distinct polarization features., Comment: 15 pages, 7 figures. Published in Physical Review D

In this paper, we introduce a novel way to represent the interface for two-phase flows with phase change. We combine a level-set method with a Cartesian embedded boundary method and take advantage of both. This is part of an effort to obtain a numerical strategy relying on Cartesian grids allowing the simulation of complex boundaries with possible change of topology while retaining a high-order representation of the gradients on the interface and the capability of properly applying boundary conditions on the interface. This leads to a two-fluid conservative second-order numerical method. The ability of the method to correctly solve Stefan problems, onset dendrite growth with and without anisotropy is demonstrated through a variety of test cases. Finally, we take advantage of the two-fluid representation to model a Rayleigh--B\'enard instability with a melting boundary.

To better understand magnetic structure and eruptive process of solar filaments, a solar active-region filament (labeled F2) eruption associated with a B-class flare was investigated by using high-resolution H$\alpha$ data from the 1 m New Vacuum Solar Telescope (NVST), combined with EUV observations of the Solar Dynamical Observatory (SDO). The filament F2 was disturbed by another filament (labeled F1) eruption that experienced a whip-like motion. Before the filament F2 eruption, the Dopplergrams show that the southern and the northern parts of the filament F2 body exhibit blueshift and redshift along the filament spine, simultaneously. It implies that the filament F2 was rolling from one side to the other. During the filament F2 eruption, the Doppler velocity shifts of the filament body are opposite to that before its eruption. It demonstrates that the filament body exhibits an untwisting motion, which can be also identified by tracing the movement of the eruptive filament threads. Moreover, it is found that the material of the filament F2 was transferred to the surrounding magnetic field loops, which is caused by magnetic reconnection between the filament F2 and the surrounding magnetic loops. According to the right-bearing threads of the filament F2 before its eruption, it can be deduced that the filament F2 is initially supported by a sheared arcade. The following observations reveal that the twisted magnetic structure of the filament F2 formed in the eruption phase., Comment: 16 pages, 7 figures, accepted for publication in ApJ

Soar filament eruptions are often associated with solar flares and coronal mass ejections (CMEs), which are the major impacts on space weather. However, the fine structures and the trigger mechanisms of solar filaments are still unclear. To address these issues, we studied a failed solar active-region filament eruption associated with a C-class flare by using high-resolution H$\alpha$ images from the New Vacuum Solar Telescope (NVST), supplemented by EUV observations of the Solar Dynamical Observatory (SDO). Before the filament eruption, a small bi-pole magnetic field emerged below the filament. And then magnetic reconnection between the filament and the emerging bi-pole magnetic field triggered the filament eruption. During the filament eruption, the untwisting motion of the filament can be clearly traced by the eruptive threads. Moreover, the foot-points of the eruptive threads are determined by tracing the descending filament materials. Note that the filament twisted structure and the right part of the eruptive filament threads cannot be seen before the filament eruption. These eruptive threads at the right part of the filament are found to be rooting in the weak negative polarities near the main negative sunspot. Moreover, a new filament formed in the filament channel due to material injection from the eruptive filament. The above observations and the potential field extrapolations are inclined to support that the filament materials were transferred into the overlying magnetic loops and the nearby filament channel by magnetic reconnection. These observations shed light on better understanding on the complexity of filament eruptions., Comment: 20 pages, 11 figures, accepted for publication in ApJ

In this letter, we present a spectacular eruptive flare (X8.2) associated with a coronal mass ejection (CME) on 2017 September 10 at the west limb of the Sun. A flux rope eruption is followed by the inflow, the formation of a current sheet and a cusp structure, which were simultaneously observed during the occurrence of this flare. The hierarchical layers of the cusp-shaped structure are well observed in 131 \AA\ observation. The scenario that can be created from these observations is very consistent with the predictions of some eruptive models. Except for the characteristics mentioned above in the process of the flare predicted by classical eruption models, the current sheet separating into several small current sheets is also observed at the final stage of the flux rope eruption. The quantitative calculation of the velocities and accelerations of the inflow, hot cusp structure, and post-flare loops is presented. The width of the current sheet is estimated to be about 3 $\times$ $10^{3}$ km. These observations are very useful to understand the process of solar eruptions., Comment: 16 pages, 5 figures, accepted for publication in ApJL

We present a clear case study on the occurrence of two successive X-class flares including a decade-class flare (X9.3) and two coronal mass ejections (CMEs) triggered by shearing motion and sunspot rotation in active region NOAA 12673 on 2017 September 6. A shearing motion between the main sunspots with opposite polarities started on September 5 and even lasted after the second X-class flare on September 6. Moreover, the main sunspot with negative polarity rotated around its umbral center and another main sunspot with positive polarity also exhibited a slow rotation. The sunspot with negative polarity at the northwest of active region also began to rotate counter-clockwise before the onset of the first X-class flare. The successive formation and eruption of two S-shaped structures were closely related to the counter-clockwise rotation of three sunspots. It is also found that the rotation of sunspots is faster during four hours prior to the onset of the flares than the period before. The existence of a flux rope is found prior to the onset of two flares by using non-linear force free field extrapolation based on the vector magnetograms observed by SDO/HMI. These results suggest that shearing motion and sunspot rotation play an important role in the buildup of the free energy and the formation of flux ropes in the corona which produces solar flares and CMEs., Comment: 28 pages, 12 figures, ApJ

Solar flares and coronal mass ejections (CMEs) are the most powerful explosions in the Sun. They are major sources of potentially destructive space weather conditions. However, the possible causes of their initiation remain controversial. By using high resolution data observed by NST of BBSO, supplemented by Solar Dynamics Observatory (SDO) observations, we present unusual observations of a small-scale emerging flux rope near a large sunspot, whose eruption produced an M-class flare and a coronal mass ejection. The presence of the small-scale flux rope was indicated by static nonlinear force free field (NLFFF) extrapolation as well as data-driven MHD modeling of the dynamic evolution of the coronal 3D magnetic field. During the emergence of the flux rope, rotation of satellite sunspots at the footpoints of the flux rope was observed. Meanwhile, the Lorentz force, magnetic energy, vertical current, and transverse fields were increasing during this phase. The free energy from the magnetic flux emergence and twisting magnetic fields is sufficient to power the M-class flare. These observations for the first time present the complete process from the emergence of the small-scale flux rope to the production of solar eruptions., Comment: 26 pages,7 figures, accepted for publication in ApJ

We present a detailed study of the formation of an inverse S-shaped filament prior to its eruption in active region NOAA 11884 from October 31 to November 2, 2013. In the initial stage, clockwise rotation of a small positive sunspot around the main negative trailing sunspot formed a curved filament. Then the small sunspot cancelled with negative magnetic flux to create a longer active-region filament with an inverse S-shape. At the cancellation site a brightening was observed in UV and EUV images and bright material was transferred to the filament. Later the filament erupted after cancellation of two opposite polarities under the upper part of the filament. Nonlinear force-free field (NLFFF) extrapolation of vector photospheric fields suggests that the filament may have a twisted structure, but this cannot be confirmed from the current observations., Comment: 26 pages, 11 figures, accepted for publication in ApJ

Study on the small-scale structures and material flows of solar quiescent filaments is very important for understanding the formation and equilibrium of solar filaments. Using the high resolution H{\alpha} data observed by the New Vacuum Solar Telescope (NVST), we present the structures of the barbs and the material flows along the threads across the spine in two quiescent filaments on 2013 September 29 and on 2012 November 2, respectively. During the evolution of the filament barb, several parallel tube-shaped structures formed and the width of the structures ranges from about 2.3 Mm to 3.3 Mm. The parallel tube-shaped structures merged together accompanied with the material flows from the spine to the barb. Moreover, the boundary between the barb and surrounding atmosphere is very neat. The counter-streaming flows were not found to appear alternately in the adjacent threads of the filament. However, the large-scale patchy counter-streaming flows are detected in the filament. The flows in one patch of the filament have the same direction and the flows in the adjacent patch have opposite directions. The patches of two opposite flows with a size of about ten arcseconds exhibited alternately along the spine of the filament. The velocity of these material flows ranges from 5.6 km/s to 15.0 km/s. The material flows along the threads of the filament did not change their direction for about two hours and fourteen minutes during the evolution of the filament. Our results confirm that the large-scale counter-streaming flows with the certain width along the threads of solar filaments exist and are well coaligned with the threads., Comment: 12 pages,5 figures, Accepted for publication in RAA

Light's wave-particle duality is at the heart of quantum mechanics and can be well illustrated by Wheeler's delayed-choice experiment. The choice of inserting or removing the second classical (quantum) beam splitter in a Mach-Zehnder interferometer determines the classical (quantum) wave-particle behaviors of a photon. In this paper, we report our experiment using the classical beam splitter to observe the simultaneous wave-particle behaviors in the wave-packet of a narrowband single photon. This observation suggests that it is necessary to generalize the current quantum wave-particle duality theory. Our experiment demonstrates that the produced wave-particle state can be considered an additional degree of freedom and can be utilized in encoding quantum information., Comment: 6 pages including Supplemental Material

To better understand the structures of active-region filaments and the eruption process, we study an active-region filament eruption in active region NOAA 11082 in detail on June 22, 2010. Before the filament eruption, the opposite unidirectional material flows appeared in succession along the spine of the filament. The rising of the filament triggered two B-class flares at the upper part of the filament. As the bright material was injected into the filament from the sites of the flares, the filament exhibited a rapid uplift accompanying the counterclockwise rotation of the filament body. From the expansion of the filament, we can see that the filament is consisted of twisted magnetic field lines. The total twist of the filament is at least 5$\pi$ obtained by using time slice method. According to the morphology change during the filament eruption, it is found that the active-region filament was a twisted flux rope and its unwinding motion was like a solar tornado. We also find that there was a continuous magnetic helicity injection before and during the filament eruption. It is confirmed that magnetic helicity can be transferred from the photosphere to the filament. Using the extrapolated potential fields, the average decay index of the background magnetic fields over the filament is 0.91. Consequently, these findings imply that the mechanism of solar filament eruption could be due to the kink instability and magnetic helicity accumulation., Comment: 26 pages,11 figures, accepted for publication in ApJ

Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider at center-of-mass energies of $\sqrt{s}=4.23$, 4.26, and 4.36~GeV, we observe $\EE\to \pphc$ for the first time. The Born cross sections are measured and found to be about half of those of $\EE\to \pi^+\pi^-h_c$ within less than 2$\sigma$. In the $\pi^0h_c$ mass spectrum, a structure at 4.02~GeV/$c^2$ is found. It is most likely to be the neutral isospin partner of the $\zcp^{\pm}$ observed in the process of $\EE\to \pi^+\pi^-h_c$ is found. A fit to the $\pi^0 h_c$ invariant mass spectrum, with the width of the $\zcpn$ fixed to that of its charged isospin partner and possible interferences with non-$\zcpn$ amplitudes neglected, gives a mass of ($4023.9\pm 2.2 \pm 3.8$)~MeV/$c^2$ for the $\zcpn$, where the first error is statistical and the second systematic., Comment: 7 pages, 2 figures

Using $1.06\times10^8$ $\psi(3686)$ events recorded in $e^{+}e^{-}$ collisions at $\sqrt{s}=$ 3.686 GeV with the BESIII at the BEPCII collider, we present searches for C-parity violation in $J/\psi \to \gamma\gamma$ and $ \gamma \phi$ decays via $\psi(3686) \to J/\psi \pi^+\pi^-$. No significant signals are observed in either channel. Upper limits on the branching fractions are set to be $\mathcal{B}(J/\psi \to \gamma\gamma) < 2.7 \times 10^{-7}$ and $\mathcal{B}(J/\psi \to \gamma\phi) < 1.4 \times 10^{-6}$ at the 90\% confidence level. The former is one order of magnitude more stringent than the previous upper limit, and the latter represents the first limit on this decay channel., Comment: 7 pages, 2 figures