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Wei-Hua Wang

Publications and source records attributed to Wei-Hua Wang.

At least 19 recordsLinked to original sources

Multi-task deep-learning optimization of trade-off properties for superior-performance Fe-based soft magnetic alloys

Fe-based amorphous alloys are promising soft magnetic materials for developing next-generation devices with high frequency and efficiency. However, optimization of Fe-based alloys with ultra-high saturation magnetic flux density (B_s), ultra-low coercivity (H_c), and good glass-forming ability is a notorious problem, owing to the vast composition space and complex trade-offs of these properties. Thus, conventional design methods encounter great challenges. Here we develop a generative multi-task deep learning (GMTDL) to achieve simultaneous optimization of compositions and trade-off properties. The GMTDL can sufficiently exploit and share the knowledge of datasets across different tasks, despite the limitation and imbalance of these datasets. Therefore, it exhibits superior performance in prediction of alloys with multiple targeted properties, outperforming previous machine learning-based design strategies. Moreover, the GMTDL can also tailor compositions, providing an efficient way to regulate properties and generate desired candidates for further experimental processing. The validity and reliability of GMTDL are rigorously tested by benchmarking with Fe-based alloys reported very recently. Moreover, some new alloys with ultra-high B_s and ultra-low H_c are predicted. The optimal content windows of key elements and their synergistic effects are also unraveled for practical guidance. Thus, our study establishes an effective and reliable paradigm for simultaneous prediction and optimization of high-performance materials with multiple properties.

cond-mat.mtrl-sci↗

Locate a stellar flare from the M dwarf LAMOST J1332+5057

Young M-type stars exhibit frequent flares, which would seriously impact their habitable planets. Since stellar surfaces cannot be resolved, flare locations remain unknown. Here, by using the Mg I b emission line in LAMOST spectra, the location of a stellar flare from a young M dwarf is pinpointed at $ (-123.0^{+8.0}_{-5.8}, 80.5^{+2.9}_{-3.2})$ in degree in the polar region. Our method can be used to accurately locate stellar flares. This would enable us to assess the impact of stellar flares on planets more accurately and improve our understanding of stellar dynamo models.

astro-ph.SR↗

Research Paradigm of Materials Science Tetrahedra with Artificial Intelligence

The classical material tetrahedron that represents the Structure-Property-Processing-Performance-Characterization relationship is the most important research paradigm in materials science so far. It has served as a protocol to guide experiments, modeling, and theory to uncover hidden relationships between various aspects of a certain material. This substantially facilitates knowledge accumulation and material discovery with desired functionalities to realize versatile applications. In recent years, with the advent of artificial intelligence (AI) techniques, the attention of AI towards scientific research is soaring. The trials of implementing AI in various disciplines are endless, with great potential to revolutionize the research diagram. Despite the success in natural language processing and computer vision, how to effectively integrate AI with natural science is still a grand challenge, bearing in mind their fundamental differences. Inspired by these observations and limitations, we delve into the current research paradigm dictated by the classical material tetrahedron and propose two new paradigms to stimulate data-driven and AI-augmented research. One tetrahedron focuses on AI for materials science by considering the Matter-Data-Model-Potential-Agent diagram. The other demonstrates AI research by discussing Data-Architecture-Encoding-Optimization-Inference relationships. The crucial ingredients of these frameworks and their connections are discussed, which will likely motivate both scientific thinking refinement and technology advancement. Despite the widespread enthusiasm for chasing AI for science, we must analyze issues rationally to come up with well-defined, resolvable scientific problems in order to better master the power of AI.

cond-mat.mtrl-sci↗

Universal quasi-degenerate orbital origin of two-dome phases in iron pnictide superconductors

A series of experiments revealed that novel bipartite magnetic and superconducting (SC) phases widely exist in the phase diagrams of iron pnictides and chalcogenides. Nevertheless, the origin of the two-dome magnetic and SC phases in iron-based compounds remains unclear. Here we theoretically investigated the electronic structures, magnetic and SC properties of three representative iron-based systems, i.e. LaFeAsO$_{1-x}$H$_{x}$, LaFeAs$_{1-x}$P$_{x}$O and KFe$_{2}$As$_{2}$. We propose a unified quasi-degenerate orbital mechanism for the emergence of the two-dome parent magnetic/structural phase and the subsequent two-dome SC phase. It is found that the degenerate in-plane anisotropic $d_{xz/yz}$ orbitals dominate the first magnetic/structural and SC phases, while in-plane isotropic orbitals $d_{xy}$ or $d_{3z^{2}-r^{2}}$ with quasi-degeneracy originating from quasi-symmetry drive the emergence of the second magnetic/SC dome phase. Moreover, a matching rule of spin and orbital modes for SC pairing state is proposed in multi-orbital iron-based systems. These results imply an orbital-driven mechanism as well as an orbital-selective scenario, and shed light on the understanding of the multi-dome magnetic and SC phases in multi-orbital systems.

cond-mat.supr-con↗

Evolution of correlated electronic states of La2NiO4 under hydrostatic pressure

We elucidate the electronic structure and quantum many-body instabilities of the monolayer nickelate La2NiO4 under hydrostatic pressure using a combination of density functional theory, dynamical mean-field theory (DFT+DMFT), and random phase approximation (RPA). Our DFT+DMFT calculations reveal non-Fermi-liquid behavior and coherence loss near the Fermi level at low pressures, driven by strong electron correlations within the Ni-e_g orbital manifold, which is analogous to the low-energy electronic properties observed in La3Ni2O7. However, multi-orbital spin susceptibility analysis demonstrates an exceptionally suppressed critical Stoner parameter U_c (about 0.4~0.7 eV), indicating robust magnetic order that dominates the ground state and precludes superconductivity in the pristine system. Below U_c, superconducting instabilities exhibit a pressure-driven symmetry transition: the d_(x2-y2)-wave pairing prevails at ambient and low pressure, while the s+g-wave symmetry occurs above 75 GPa. This transition is attributed to pressure-induced self-doping effect. The high-angular-momentum g-wave component incurs significant energetic penalties, rendering high-Tc superconductivity unlikely. We conclude that the absence of superconductivity in La2NiO4 arises from its robust intrinsic magnetism and the unfavorable pairing symmetry under pressure, suggesting that alternative routes-such as chemical doping or epitaxial strain-are necessary to suppress magnetism and unlock superconducting states.

cond-mat.str-el↗

The persistent shift in spin-down rate following the largest Crab pulsar glitch rules out external torque variations due to starquakes

It was previously believed that, the long-term persistent increase in the spin-down rate of the Crab pulsar following a glitch is direct evidence of a starquake-induced glitch or at least related to a starquake. Using radio data covering 1710 days following the 2017 glitch, we obtain an extreme persistent increase of the spin-down rate, which allows to test two prevailing models related to starquake through an interrelation analysis between glitch size (the amplitude of the frequency step at a glitch) and persistent increase in the spin-down rate of the star. Our results do not support the hypothesis that glitches induce the external torque variation of the Crab pulsar, which may indicate no occurrence of starquake during the Crab pulsar glitch. This can explain why no changes in the radio and X-ray flux, pulse profile and spectrum of the Crab pulsar have been observed. We also suggest an internal mechanism due to superfluidity as an explanation for the long-term persistent shift in spin-down rate of the Crab pulsar following the relatively large glitches.

astro-ph.HE↗

Efficient light upconversion via resonant exciton-exciton annihilation of dark excitons in few-layer transition metal dichalcogenides

In this work, we report a pronounced light upconversion in few-layer transition metal dichalcogenides. Our joint theory-experiment study attributes the upconversion photoluminescence to a resonant exciton-exciton annihilation involving a pair of dark excitons with opposite momenta, followed by the spontaneous emission of upconverted bright excitons, which can have a high upconversion efficiency. Additionally, the upconversion photoluminescence is generic in MoS2, MoSe2, WS2, and WSe2, showing a high tuneability from green to ultraviolet light.

cond-mat.mtrl-sci↗

The white-light superflares from cool stars in GWAC triggers

M-type stars are the ones that flare most frequently, but how big their maximum flare energy can reach is still unknown. We present 163 flares from 162 individual M2 through L1-type stars that triggered the GWAC, with flare energies ranging from $10^{32.2}$ to $10^{36.4}$ erg . The flare amplitudes range from $\triangle G = 0.84$ to $\sim 10$ mag. Flare energy increases with stellar surface temperature ($T_{\rm eff}$) but both $\triangle G$ and equivalent duration $\log_{10}(ED)$ seem to be independent of $T_{\rm eff}$. Combining periods detected from light curves of TESS and K2, spectra from LAMOST, SDSS and the 2.16 m Telescope, and the Gaia DR3 data, we found that these GWAC flare stars are young. For the stars that have spectra, we found that these stars are in or very near to the saturation region, and $\log_{10}(L_{\rm Hα}/L_{\rm bol})$ is lower for M7-L1 stars than for M2-M6 stars. We also studied the relation between GWAC flare bolometric energy $E_{\rm bol}$ and stellar hemispherical area $S$, and found that $\log_{10}E_{\rm bol}$ (in erg) increases with increasing $S$ (in cm$^2$), and the maximum flare energy $\log_{10}E_{\rm bol, max} \geqslant \log_{10}S + 14.25$. For M7-L1 stars, there seem to be other factors limiting their maximum flare energies in addition to stellar hemispherical area.

astro-ph.SR↗

Three-dimensional atomic interface between metal and oxide in Zr-ZrO2 nanoparticles

Metal-oxide interfaces with poor coherency have unique properties comparing to the bulk materials and offer broad applications in the fields of heterogeneous catalysis, battery, and electronics. However, current understanding of the three-dimensional (3D) atomic metal-oxide interfaces remains limited because of their inherent structural complexity and limitations of conventional two-dimensional imaging techniques. Here, we determine the 3D atomic structure of metal-oxide interfaces in zirconium-zirconia nanoparticles using atomic-resolution electron tomography. We quantitatively analyze the atomic concentration and the degree of oxidation, and find the coherency and translational symmetry of the interfaces are broken. Moreover, we observe porous structures such as Zr vacancies and nano-pores and investigate their distribution. Our findings provide a clear 3D atomic picture of metal-oxide interface with direct experimental evidence. We anticipate this work could encourage future studies on fundamental problems of oxides such as interfacial structures in semiconductor and atomic motion during oxidation process.

cond-mat.mtrl-sci↗

Results of 23 yr of Pulsar Timing of PSR J1453-6413

In this paper, we presented the 23.3 years of pulsar timing results of PSR J1456-6413 based on the observation of Parkes 64m radio telescope. We detected two new glitches at MJD 57093(3) and 59060(12) and confirmed its first glitch at MJD 54554(10). Using the "Cholesky" timing analysis method, we have determined its position, proper motion, and two-dimensional transverse velocities from the data segments before and after the second glitch, respectively. Furthermore, we detected exponential recovery behavior after the first glitch, with a recovery time scale of approximately 200 days and a corresponding exponential recovery factor Q of approximately 0.15(2), while no exponential recovery was detected for the other two glitches. More interestingly, we found that the leading component of the integral pulse profile after the second glitch became stronger, while the main component became weaker. Our results will expand the sample of pulsars with magnetosphere fluctuation triggered by the glitch event.

astro-ph.HE↗

Possible high-temperature magnetically topological material Mn$_{3}$Bi$_{2}$Te$_{6}$

The Mn-Bi-Te family displaying magnetism and non-trivial topological properties has received extensive attention. Here, we predict that the antiferromagnetic structure of Mn$_{3}$Bi$_{2}$Te$_{6}$ with three MnTe layers is energetically stable and the magnetic coupling strength of Mn-Mn is enhanced four times compared with that in the single MnTe layer of MnBi$_{2}$Te$_{4}$. The predicted Néel transition point is higher than 77 K, the liquid-nitrogen temperature. The topological properties show that with the variation of the MnTe layer from a single layer to three layers, the system transforms from a nontrivial topological phase to a trivial topological phase. Interestingly, the ferromagnetic state of Mn$_{3}$Bi$_{2}$Te$_{6}$ is a topological semimetal and it exhibits a topological transition from trivial to nontrivial induced by the magnetic transition. Our results enrich the Mn-Bi-Te family system, offer a new platform for studying topological phase transitions, and pave a new way to improve the working temperature of magnetically topological devices.

cond-mat.str-el↗

On torque reversal during delayed spin up glitch of SGR 1935+2154

Ge et al. reported a peculiar large glitch observed from SGR 1935 recently~\citep{2022arXiv221103246G}. % Interestingly, this glitch occurred about $3.1\pm 2.5~\rm{days}$ before FRB 200428, accompanied by a delayed spin up (DSU) process with a timescale of $8\pm 1~\rm{days}$. % This DSU is the first one detected from magnetars unambiguously, previously, DSU has only been detected from large glitches of the young Crab pulsar. % Strikingly, this DSU even resulted in torque reversal, i.e., the spin down state of SGR 1935 was turned into a spin up one within $8\pm 1~\rm{days}$, the first case observed from isolated neutron stars as far as we know. % What's more, the average positive torque is consistent in value and order of magnitude with those deduced from DSUs observed from the Crab pulsar. % The coincidences of DSU appearance and consistent positive torque in the Crab pulsar and SGR 1935 suggest that, these DSUs have the same physical origin and should be analyzed simultaneously. % Joint analysis on DSUs from the Crab pulsar and SGR 1935 suggests a physical origin independent of (at least not directly dependent on) rotational parameters. % If this new DSU and torque reversal phenomena be further confirmed and accretion be excluded convincingly, nearly all models regarding DSU phenomenon under the framework of vortex motion should be reconsidered, new physics will be required. % We stress that, joint analysis on DSUs from different pulsars with different rotational parameters may provide pivotal clue to reveal their physical origin, even neutron star equation of state and the triggering mechanism(s) of (galactic) fast radio bursts ultimately.

astro-ph.HE↗

Topology of vibrational modes predict plastic events in glasses

The plastic deformation of crystalline materials can be understood by considering their structural defects such as disclinations and dislocations. Although glasses are also solids, their structure resembles closely the one of a liquid and hence the concept of structural defects becomes ill-defined. As a consequence it is very challenging to rationalize on a microscopic level the mechanical properties of glasses close to the yielding point and to relate plastic events with structural properties. Here we investigate the topological characteristics of the eigenvector field of the vibrational excitations of a two-dimensional glass model, notably the geometric arrangement of the topological defects as a function of vibrational frequency. We find that if the system is subjected to a quasistatic shear, the location of the resulting plastic events correlate strongly with the topological defects that have a negative charge. Our results provide thus a direct link between the structure of glasses prior their deformation and the plastic events during deformation.

cond-mat.dis-nn↗

Cycle deformation enabled controllable mechanical polarity of bulk metallic glasses

Tuning anisotropy in bulk metallic glasses, ideally isotropic, is of practical interest in optimizing properties and of fundamental interest in understanding the amorphous structure and its instability. By employing the quasi-elastic asymmetric mechanical cycling method, we effectively induce the mechanical polarity of a model bulk metallic glass, without damaging the sample or introducing significant annealing or rejuvenation effects. Moreover, the polarized anelastic limit can be well controlled by regulating the amplitude of mechanical cycling. Through the atomic-level analysis of nonaffine displacement, we find that only plastic atomic rearranged events corresponding to the training direction can be exhausted by asymmetric cycling and the survived anelastic events dominate the directional anelastic limit. The polarized distribution of local yield stress reveals that the mechanical polarity is attributed to the plastic-event-healing induced asymmetry of local potential energy surface, rather than frozen-in anelastic strain. Furthermore, the healing of plastic events associated with the redistribution of local residual stress indicates the origin of polarity induced by asymmetric cycling. Our study is of fundamental importance, which furthers our understanding of the mechanical deformation of metallic glasses and shed some light on the prospects for improved properties through induced anisotropy.

cond-mat.mtrl-sci↗

Constraining mechanism associated with fast radio burst and glitch from SGR J1935

The discovery of fast radio burst (FRB) 200428 from galactic SGR J1935+2154 makes it possible to measure rotational changes accompanied by FRBs and to test several FRB models which may be simultaneously associated with glitches. Inspired by this idea, we present order of magnitude calculations to the scenarios proposed. FRB models such as global starquakes, crust fractures and collisions between pulsars and asteroids/comets are discussed. For each mechanism, the maximum glitch sizes are constrained by the isotropic energy release during the X-ray burst and/or the SGR J1935+2154-like radio burst rate. Brief calculations show that, the maximum glitch sizes for different mechanisms differ by order(s) of magnitude. If glitches are detected to be coincident with FRBs from galactic magnetars in the future, glitch behaviors (such as glitch size, rise timescale, the recovery coefficient and spin down rate offset) are promising to serve as criterions to distinguish glitch mechanisms and in turn to constrain FRB models.

astro-ph.HE↗

Oxidized-monolayer Tunneling Barrier for Strong Fermi-level Depinning in Layered InSe Transistors

In 2D-semiconductor-based field-effect transistors and optoelectronic devices, metal-semiconductor junctions are one of the crucial factors determining device performance. The Fermi-level (FL) pinning effect, which commonly caused by interfacial gap states, severely limits the tunability of junction characteristics, including barrier height and contact resistance. A tunneling contact scheme has been suggested to address the FL pinning issue in metal-2D-semiconductor junctions, whereas the experimental realization is still elusive. Here, we show that an oxidized-monolayer-enabled tunneling barrier can realize a pronounced FL depinning in indium selenide (InSe) transistors, exhibiting a large pinning factor of 0.5 and a highly modulated Schottky barrier height. The FL depinning can be attributed to the suppression of metal- and disorder-induced gap states as a result of the high-quality tunneling contacts. Structural characterizations indicate uniform and atomically thin surface oxidation layer inherent from nature of van der Waals materials and atomically sharp oxide-2D-semiconductor interfaces. Moreover, by effectively lowering the Schottky barrier height, we achieve an electron mobility of 2160 cm$^2$/Vs and a contact barrier of 65 meV in two-terminal InSe transistors. The realization of strong FL depinning in high-mobility InSe transistors with the oxidized monolayer presents a viable strategy to exploit layered semiconductors in contact engineering for advanced electronics and optoelectronics.

cond-mat.mes-hall↗

Emergence and percolation of rigid domains during colloidal glass transition

Using video microscopy, we measure local spatial constraints in disordered binary colloidal samples, ranging from dilute fluids to jammed glasses, and probe their spatial and temporal correlations to local dynamics during the glass transition. We observe the emergence of significant correlations between constraints and local dynamics within the Lindemann criterion, which coincides with the onset of glassy dynamics in supercooled liquids. Rigid domains in fluids are identified based on local constraints, and demonstrate a percolation transition near glass transition, accompanied by the emergence of dynamical heterogeneities. Our results show that the spatial constraints instead of the geometry of amorphous structures is the key that connects the complex spatial-temporal correlations in disordered materials.

cond-mat.soft↗

Magnetic borophenes from evolutionary search

A computation methodology based on ab initio evolutionary algorithms and the spin-polarized density functional theory was developed to predict two-dimensional (2D) magnetic materials. Its application to a model system borophene reveals an unexpected rich magnetism and polymorphism. A stable borophene with nonzero thickness was an antiferromagnetic (AFM) semiconductor from first-principles calculations, which can be further turned into a half metal by finite electron doping. In this borophene, the buckling and coupling among three atomic layers are not only responsible for the magnetism, but also result in an out-of-plane negative Poissons ratios under uniaxial tension, making it the first elemental material possessing auxetic and magnetic properties simultaneously.

cond-mat.mtrl-sci↗