Strong Magnetic Field Research Articles

Magnetic coupling through flux branching of adjacent type-I and -II superconductors in a neutron star

Abstract The inner and outer cores of neutron stars are believed to contain type-I and -II proton superconductors, respectively. The type-I superconductor exists in an intermediate state, comprising macroscopic flux-free and flux-containing regions, while the type-II superconductor is flux-free, except for microscopic, quantized flux tubes. Here, we show that the inner and outer cores are coupled magnetically, when the macroscopic flux tubes subdivide dendritically into quantized flux tubes, a phenomenon called flux branching. An important implication is that up to ∼1012(r1/106 cm) erg of energy are required to separate a quantized flux tube from its progenitor macroscopic flux tube, where r1 is the length of the macroscopic flux tube. Approximating the normal-superconducting boundary as sharp, we calculate the magnetic coupling energy between a quantized and macroscopic flux tube due to flux branching as a function of, f1, the radius of the type-I inner core divided by the radius of the type-II outer core. Strong coupling delays magnetic field decay in the type-II superconductor. For an idealised inner core containing only a type-I proton superconductor and poloidal flux, and in the absence of ambipolar diffusion and diamagnetic screening, the low magnetic moments (≲ 1027 G cm3) of recycled pulsars imply f1 ≲ 10−1.5.

On the initial spin periods of magnetars born in weak supernova explosions and their gravitational wave radiation

The initial spin periods of newborn magnetars are strongly associated with the origin of their strong magnetic fields, both of which can affect the electromagnetic radiation and gravitational waves (GWs) emitted at their birth. Combining the upper limit ESNR≲1051\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_{\ extrm{SNR}}\\lesssim 10^{51}$$\\end{document} erg on the explosion energies of the supernova (SN) remnants around slowly-spinning magnetars with a detailed investigation on the evolution of newborn magnetars, we set constraints on the initial spin periods of magnetars born in weak SN explosions. Depending on the conversion efficiency η\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta $$\\end{document} of the electromagnetic energy of these newborn magnetars into the kinetic energy of SN ejecta, the minimum initial spin periods of these newborn magnetars are Pi, min≃5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P_{\ extrm{i, min}}\\simeq 5$$\\end{document}–6 ms for an ideal efficiency η=1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta =1$$\\end{document}, Pi, min≃3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P_{\ extrm{i, min}}\\simeq 3$$\\end{document}–4 ms for a possible efficiency η=0.4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta =0.4$$\\end{document}, and Pi, min≃1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P_{\ extrm{i, min}}\\simeq 1$$\\end{document}–2 ms for a relatively low efficiency η=0.1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta =0.1$$\\end{document}. Based on these constraints and adopting reasonable values for the physical parameters of the newborn magnetars, we find that their GW radiation at νe,1=ν\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u _{\ extrm{e,1}}=\ u $$\\end{document} may be undetectable by the Einstein Telescope (ET) since the maximum signal-to-noise ratio (S/N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{S/N}$$\\end{document}) is only 2.41 even the sources are located at a very close distance of 5 Mpc, where ν\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u $$\\end{document} are the spin frequencies of the magnetars. At such a distance, the GWs emitted at νe,2=2ν\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u _{\ extrm{e,2}}=2\ u $$\\end{document} from the newborn magnetars with dipole fields Bd=5×1014\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_{\ extrm{d}}=5\ imes 10^{14}$$\\end{document} and 1015\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{15}$$\\end{document} G may be detectable by the ET because S/N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{S/N}$$\\end{document} are 10.01 and 19.85, respectively. However, if these newborn magnetars are located at 20 Mpc away in the Virgo supercluster, no GWs could be detected by the ET due to low S/N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{S/N}$$\\end{document}.

Internal inspection method for crack defects in ferromagnetic pipelines under remanent magnetization

Magnetic flux leakage (MFL) testing is effective in detecting corrosion in ferromagnetic pipelines. However, the MFL generated at the crack is highly weak and is easily drowned in the strong background magnetic field and difficult to detect. Therefore, this paper creatively proposes a remanent magnetic flux leakage (RMFL) detection method. This method utilizes the hysteresis state of the pipeline after MFL detection and identifies crack defects by collecting the remanent magnetic flux density near the inner wall surface of the pipeline. The remanent magnetic field distribution near the pipeline surface is examined at different crack sizes, magnetization speeds, and lift-off values via theoretical analysis, finite element simulation, and experimental verification. In addition, experiments have demonstrated that in terms of crack detection capability, RMFL is superior to MFL. Therefore, adding a RMFL measurement module to the conventional MFL detector has important practical value. It can realize the targeted collaborative application of these two technologies, namely the synchronous detection of corrosion and crack defects, which greatly improves the detection coverage and detection efficiency.

Modeling magnetic field amplification in supernova remnants driven by laser

Abstract The origin of magnetic fields and their amplification have always been hot topics in fields such as astrophysics and high-energy-density physics. Among them, the turbulent dynamo effect is an important candidate mechanism, and the interaction between supernova remnants (SNRs) is an important carrier for studying the amplification effect of turbulent magnetic fields. In this paper, we use the radiation magnetohydrodynamic simulation program to carry out a scaling simulation study on the amplification effect of turbulent magnetic fields in the interaction of SNRs driven by powerful lasers. We investigate and compare the evolution of turbulence under different laser driving methods, different directions, and different intensities of initial external environmental magnetic fields. Here, we carefully identify the contributions of Biermann self-generated magnetic fields and environmental magnetic fields in the process of magnetic field amplification, present magnetic energy spectra, and magnetic field amplification factors, and analyze the influence of radiative cooling effect on turbulence and magnetic field evolution. The results show that the collision direction component of the environmental magnetic field dominates the process of magnetic field amplification, and the frequency spectrum of turbulence is consistent with Kolmogorov’s law. The research results are necessary for sorting out and elucidating the physical mechanism of magnetic field amplification in SNRs, and have reference significance for regulating turbulence in strong magnetic fields in the future.

Thermal gradient-induced critical current degradation in mesoscopic superconducting thin film

Abstract Superconducting materials inevitably suffer from the sudden change of temperature in the localized areas in practical applications, the concomitant thermal gradient might be detrimental to the performance. Critical current density is a key factor affecting the performance of superconductors, however, the effect of thermal gradient on the critical current density has not been identified. Here, combining the time-dependent Ginzburg-Landau (TDGL) equations and the heat transfer equation, the thermal gradient and magnetic field dependence of critical current density are systematically investigated and rationalized by exploring the behavior of vortex and magnetization. For lower magnetic fields, it is found that the thermal gradients strongly reduce the local surface barriers which inhibit vortex entry and movement, leading to a rapid deterioration of the current-carrying capability. Under moderate magnetic fields, the critical current density corresponding to higher thermal gradients decreases more slowly with increasing magnetic field, which results from the thermal gradient-induced entry and moving of vortices along the current direction. As the magnetic field continues to increase, the variation of critical current density transitions into a platform period and even slightly rises. The enhanced critical current is primarily attributed to the excess entry of vortices, which increases the surface barrier of the sample. With the further increase of the magnetic field, the critical current density continues to decrease due to increased magnetic field penetration. These results unveil the fundamental interplay among the thermal gradients, external magnetic field, vortex, magnetization, and critical current density, and provide a theoretical basis for understanding the heat-induced quench of the mesoscopic superconducting thin film in practical applications.

Machine learning assisted screening of two dimensional chalcogenide ferromagnetic materials with Dzyaloshinskii Moriya interaction

Magnetic skyrmions are potential candidates for high-density storage and logic devices because of their inherent topological stability and nanoscale size. Two-dimensional (2D) Janus transition metal chalcogenides (TMDs) are widely used to induce skyrmions due to the breaking of inversion symmetry. However, the experimental synthesis of Janus TMDs is rare, which indicates that the Janus configuration might not be the most stable MXY structure. Here, through machine-learning-assisted high-throughput first-principles calculations, we demonstrate that not all MXY compounds can be stabilized in Janus layered structure and a large proportion prefer to form other configurations with lower energy than the Janus configuration. Interestingly, these new configurations exhibit a strong Dzyaloshinskii–Moriya interaction (DMI), which can generate and stabilize skyrmions even under a strong magnetic field. This work provides not only an efficient method for obtaining ferromagnetic materials with strong DMI but also a theoretical guidance for the synthesis of TMDs via experiments.

Blue large-amplitude pulsators formed from the merger of low-mass white dwarfs

Blue large-amplitude pulsators (BLAPs) are a recently discovered group of hot stars pulsating in radial modes. Their origin needs to be explained, and several scenarios for their formation have already been proposed. We investigate whether BLAPs can originate as the product of a merger of two low-mass white dwarfs (WDs) and estimate how many BLAPs can be formed in this evolutionary channel. We used the Modules for Experiments in Stellar Astrophysics (MESA) code to model the merger of three different double extremely low-mass (DELM) WDs and the subsequent evolution of the merger product. We also performed a population synthesis of Galactic DELM WDs using the COSMIC code. We find that BLAPs can be formed from DELM WDs provided that the total mass of the system ranges between 0.32 and 0.7\,M$_ BLAPs born in this scenario either do not have any thermonuclear fusion at all or show off-centre He burning. The final product evolves to hot subdwarfs and eventually finishes its evolution either as a cooling He WD or a hybrid He/CO WD. The merger products become BLAPs only a few thousand years after coalescence, and it takes them 20\,--\,70 thousand years to pass the BLAP region. We found the instability of the fundamental radial mode to be in fair agreement with observations, but we also observed instability of the radial first overtone. The calculated evolutionary rates of period change can be both positive and negative. From the population synthesis, we found that up to a few hundred BLAPs born in this scenario can exist at present in the Galaxy. Given the estimated number of BLAPs formed in the studied DELM WD merger scenario, there is a good chance to observe BLAPs that originated through this scenario. Since strong magnetic fields can be generated during mergers, this scenario could lead to the formation of magnetic BLAPs. This fits well with the discovery of two likely magnetic BLAPs whose pulsations can be explained in terms of the oblique rotator model.

Experimental characterization of coherent states in turbulent magnetohydrodynamic pipe flow

Investigating magnetohydrodynamic (MHD) flows, whether through experimental or numerical study, presents significant challenges. A minimum requirement for experimentally studying MHD flows using optical measurement methods is the use of highly conductive, transparent fluids and strong magnetic fields in close proximity to the flow confinement. In response to these complexities, this work introduces a large-scale pipe rig setup, integrating a magnetic frame structure with a Stereoscopic Particle Image Velocimetry system for MHD flow field characterizations. This allows for the detailed analysis of coherent flow patterns under conditions of fully developed MHD turbulence. In alignment with earlier numerical studies on turbulent MHD pipe flow, our research confirms that low Hartmann number turbulence statistics are minimally affected by the applied magnetic field. Nevertheless, we show that the magnetic field significantly extends the streamwise extent of detected coherent organizational states, while their wave number distribution and morphology largely remain unchanged.

Massive Star Formation Starts in Subvirial Dense Clumps Unless Resisted by Strong Magnetic Fields

Knowledge of the initial conditions of high-mass star formation is critical for theoretical models, but are not well observed. Built on our previous characterization of a Galaxy-wide sample of 463 candidate high-mass starless clumps (HMSCs), here we investigate the dynamical state of a representative subsample of 44 HMSCs (radii 0.13–1.12 pc) using Green Bank Telescope NH3 (1,1) and (2,2) data from the Radio Ammonia Mid-Plane Survey pilot data release. By fitting the two NH3 lines simultaneously, we obtain velocity dispersion, gas kinetic temperature, NH3 column density and abundance, Mach number, and virial parameter. Thermodynamic analysis reveals that most HMSCs have Mach number <5, inconsistent with what have been considered in theoretical models. All but one (43 out of 44) of the HMSCs are gravitationally bound with virial parameter α vir < 2. Either these massive clumps are collapsing or magnetic field strengths of 0.10–2.65 mG (average 0.51 mG) would be needed to prevent them from collapsing. The estimated B-field strength correlates tightly with density, Best/mG=0.269(nH2/104cm−3)0.61 , with a similar power-law index as found in observations but a factor of 4.6 higher in strength. For the first time, the initial dynamical state of high-mass formation regions has been statistically constrained to be subvirial, in contradiction to theoretical models in virial equilibrium and in agreement with the lack of observed massive starless cores. The findings urge future observations to quantify the magnetic field support in the prestellar stage of massive clumps, which has rarely been explored so far, toward a full understanding of the physical conditions that initiate massive star formation.

Paired fermions in strong magnetic fields and daughters of even-denominator Hall plateaus

Paired fermions in strong magnetic fields and daughters of even-denominator Hall plateaus

Effect of a longitudinal magnetic field on streamer propagation in air: Numerical simulation

Two-dimensional numerical simulation of the negative streamer propagation in external electric and magnetic fields is performed for the case when applied electric and magnetic field vectors are parallel to the symmetry axis of the problem. The calculations are performed for air (a mixture of 80% N2 and 20% O2) with a concentration of gas molecules equal to Loshmidt's number. It is shown that the presence of a longitudinal field leads to a noticeable increase in the streamer propagation velocity associated with a decrease in its radius, which agrees with the known analytical estimates.

Enhanced Joule heat release at surface irregularities

The heat release that occurs in a cylindrical conductor carrying an alternating current is analyzed for the cases when the conductor has axisymmetric surface irregularities of one of three types: local bumps, local pits, and sequences of alternating bumps and pits (wavy irregularities). The magnetic field and current density distributions over the conductor cross section have been simulated. The simulation parameters were chosen to match the conditions of experiments on the generation of strong magnetic fields. However, due to the analysis of the initial heating stage, the problem is solved neglecting the temperature dependence of the resistivity of the material. A multiple increase in heat release power in the vicinity of a surface irregularity has been revealed for the three types of irregularities.

An asynchronous dual-foot inertial piezoelectric actuator with strong magnetic compatibility

To address the limitations in actuator selection within strong magnetic environments, this study introduces a novel inertial piezoelectric actuator with asynchronous dual-foot motion, which meets the need for high-precision actuation in strong magnetic field environments. The design principle is to use two driving feet that generate elliptical motion in an alternating method to achieve continuous linear motion of the actuator. This approach enhances load capacity, speed, and stepping characteristics. The design allows for better control of backward motion without modifying the driving waveform, thus improving the actuator's speed and ensuring consistent performance in both directions. A finite element model of the proposed actuator stator is developed and analyzed using commercial software to optimize its dimensional parameters. A prototype is fabricated, and experimental investigations are carried out. The results indicate that the dual asynchronous driving method significantly increases the speed of the actuator and the consistency of the motion by improving stepping characteristics. The prototype reached a maximum speed of 8.98mm/s, supported a maximum load of 4.5N, and achieved a displacement resolution of 19nm. Finally, the strong magnetic field environmental test and MRI image quality test were conducted, and experimental results confirmed that the actuator has superior magnetic compatibility, highlighting its potential for precision applications in challenging environments. This research proposes new methods to enhance the retraction characteristics and output performance of inertial actuators, with their excellent magnetic field compatibility anticipated to be applied in future MRI-compatible injectors, puncture devices, or other actuating mechanisms.

Correlation between magnetic and electrical properties of the superparamagnetic La0.6Ca0.4MnO3 compound

In this research work, we investigated the correlation between the electrical and magnetic properties of the superparamagnetic compound La0.6Ca0.4MnO3(S0C1) prepared by the citric-gel method. The confrontation of the experimental data with the theoretical models revealed that the conduction at low temperatures, in the ferromagnetic metallic (FMM) phase, can be mainly described by electron–electron (e-e) and electron-magnon (e-m) interactions. The contribution of the (e-m) interaction, became weak for strong magnetic fields. At high temperatures, in the paramagnetic semiconductor (PMSC) phase, the thermally activated hopping (TAH) model proved to be the most appropriate to fit the experimental data. To describe the resistivity behavior in a wide temperature range including the phase transition region between the (FMM) and (PMSC) phases, we adopted the percolation model, based on the phase segregation mechanism.

Numerical analysis of resonant axion-photon mixing

Many present-day axion searches attempt to probe the mixing of axions and photons, which occurs in the presence of an external magnetic field. While this process is well understood in a number of simple and idealized contexts, a strongly varying or highly inhomogeneous background can impact the efficiency and evolution of the mixing in a nontrivial manner. In an effort to develop a generalized framework for analyzing axion-photon mixing in arbitrary systems, we focus in this work on directly solving the axion-modified form of Maxwell’s equations across a simulation domain with a spatially varying background. We concentrate specifically on understanding resonantly enhanced axion-photon mixing in a highly magnetized plasma, which is a key ingredient for developing precision predictions of radio signals emanating from the magnetospheres of neutron stars. After illustrating the success and accuracy of our approach for simplified limiting cases, we compare our results with a number of analytic solutions recently derived to describe mixing in these systems. We find that our numerical method demonstrates a high level of agreement with one, but only one, of the published results. Interestingly, our method also recovers the mixing between the axion and magnetosonic-t and Alfvén modes; these modes cannot escape from the regions of dense plasma but could nontrivially alter the dynamics in certain environments. Future work will focus on extending our calculations to study resonant mixing in strongly variable backgrounds, mixing in generalized media (beyond the strong magnetic field limit), and the mixing of photons with other light bosonic fields, such as dark photons. Published by the American Physical Society 2024

Unraveling the Hybrid Origins of the X-Ray Nonthermal Emission from IGR J17091–3624

We present a comprehensive study based on multiwavelength observations from the NuSTAR, NICER, Swift, Fermi, NEOWISE, and ATCA telescopes during the 2022 outburst of the black-hole X-ray binary IGR J17091–3624. Our investigation concentrates on the heartbeat-like variability in the X-ray emission, with the aim of using it as a tool to unravel the origin of the nonthermal emission during the heartbeat state. Through X-ray timing and spectral analysis, we observe that the heartbeat-like variability correlates with changes in the disk temperature, supporting the disk radiation pressure instability scenario. Moreover, in addition to a Comptonization component, our time-averaged and phase-resolved spectroscopy reveal the presence of a power-law component that varies independently from the disk component. Combined with the radio–X-ray spectral energy distribution fitting, our results suggest that the power-law component could originate from synchrotron self-Compton radiation in the jet, which requires a strong magnetic field of about B = (0.3–3.5) × 106 G. Additionally, assuming that IGR J17091-3624 and GRS 1915 + 105 share the same radio–X-ray correlation coefficient during both the hard and the heartbeat states, we obtain a distance of 13.7 ± 2.3 kpc for IGR J17091–3624.

Tidal Disruption of a Star on a Nearly Circular Orbit

We consider Roche lobe overflow (RLO) from a low-mass star on a nearly circular orbit, onto a supermassive black hole (SMBH). If mass transfer is unstable, its rate accelerates in a runaway process, resulting in highly super-Eddington mass accretion rates, accompanied by an optically thick outflow emanating from the SMBH vicinity. This produces a 1–4 week long, bright optical/ultraviolet flare, accompanied by a 1–10 year long X-ray precursor and post-cursor emitted from the accretion flow onto the SMBH. Such “Circular Tidal Disruption Events” (TDEs) represent a new class of nuclear transients, occurring at up to 1%–10% of the canonical parabolic tidal disruption event rate. Near-breakup rotation and strong tidal deformation of the star prior to disruption could lead to strong magnetic fields, making circular TDEs possible progenitors of jetted TDEs. Outflows prior to the final stellar disruption produce a circumnuclear environment (CNM) with ∼10−2 M⊙ at distances of ∼0.01–0.1 pc, likely leading to bright radio emission, and also similar to the CNM inferred for jetted TDEs. We discuss broader connections between circular TDEs and other recently identified classes of transients associated with galactic nuclei, such as repeating TDEs and quasi-periodic X-ray eruptions, as well as possible connections to luminous fast blue optical transients such as AT2018cow. We also discuss observational signatures of the analogous RLO of a white dwarf around an intermediate-mass BH, which may be a multimessenger source in the LISA era.

Orbital Hall Effect Accompanying Quantum Hall Effect: Landau Levels Cause Orbital Polarized Edge Currents

The quantum Hall effect emerges when two-dimensional samples are subjected to strong magnetic fields at low temperatures: Topologically protected edge states cause a quantized Hall conductivity in multiples of e2/h. Here we show that the quantum Hall effect is accompanied by an orbital Hall effect. Our quantum mechanical calculations fit well the semiclassical interpretation in terms of “skipping orbits.” The chiral edge states of a quantum Hall system are orbital polarized akin to a hypothetical orbital version of the quantum anomalous Hall effect in magnetic systems. The orbital Hall resistivity scales quadratically with the magnetic field, making it the dominant effect at high fields. Published by the American Physical Society 2024

The observational evidence that all microflares that accelerate electrons to high energies are rooted in sunspots

In general, large solar flares are more efficient at accelerating high-energy electrons than microflares. Nonetheless, sometimes microflares that accelerate electrons to high energies are observed. Their origin is unclear. We statistically characterized microflares with strikingly hard spectra in the hard X-ray (HXR) range, which means that they are efficient at accelerating high-energy electrons. We refer to these events as "hard microflares." We selected 39 hard microflares, based on their spectral hardness estimated from the Solar Orbiter/STIX HXR quicklook light curves in two energy bands. The statistical analysis is built on spectral and imaging information from STIX combined with extreme ultraviolet (EUV) and magnetic field maps from SDO/AIA and SDO/HMI. The key observational result is that all hard microflares in this dataset have one of the footpoint rooted directly within a sunspot (either in the umbra or the penumbra). This clearly indicates that the underlying magnetic flux densities are large. For the events with the classic two-footpoints morphology, the absolute value of the mean line-of-sight magnetic flux density (and vector magnetic field strength) at the footpoint rooted within the sunspot ranges from 600 to 1800 G (1500 to 2500 G), whereas the outer footpoint measures from 10 to 200 G (100 to 400 G), therefore about ten times weaker. In addition, approximately 78&lt;!PCT!&gt; of the hard microflares, which exhibited two HXR footpoints, have similar or even stronger HXR flux from the footpoint rooted within the sunspot. This contradicts the magnetic mirroring scenario. The median footpoint separation, measured through HXR observations, is approximately 24 Mm, which aligns with regular events of similar GOES classes. In addition, about 74&lt;!PCT!&gt; of the events could be approximated by a single-loop geometry, demonstrating that hard microflares typically have a relatively simple morphology. Out of these events, around 54&lt;!PCT!&gt; exhibit a relatively flat flare loop geometry. We conclude that all hard microflares are rooted in sunspots, which implies that the magnetic field strength plays a key role in efficiently accelerating high-energy electrons, with hard HXR spectra associated with strong fields. This key result will allow us to further constrain our understanding of the electron acceleration mechanisms in flares and space plasmas.

Skyrmion dynamics in attractive and repulsive local magnetic fields

The study of the behavior of magnetic skyrmions in local magnetic fields’ nanometric length-scale has gained increasing interest in recent years due to the theoretical proposal of magnetic skyrmion–superconducting vortex pairs as potential hosts for topologically protected bound states, which hold high promise for applications in quantum computing. From a magnetic interaction point-of-view, the key interest lies in understanding the skyrmion dynamics triggered by the magnetic energy landscape generated by the superconducting vortex. Here, we present a micromagnetic study of the dynamics of nanometric skyrmions inside a Gaussian magnetic field profile, which is used as a simplified version of the vortex magnetic flux. On the one hand, our calculations show that local non-linear magnetic fields can be very effective in controlling the dynamics of magnetic skyrmions; in particular, they offer the appealing possibility to manipulate skyrmions in a two dimensional space. On the other hand, they also show that the dynamics of a skyrmion in a local magnetic field can be manipulated via a uniform external magnetic field without any change in the magnetic field gradient. An analytical expression for the skyrmion velocity is given, and the corresponding microscopic dynamics are confirmed by the micromagnetic simulations. This work is expected to motivate more theoretical and experimental studies of the behavior of magnetic skyrmions in proximity to superconducting vortices.