Spin Model Research Articles

Electropositive Magnetic Fluorescent Nanoprobe-Mediated Immunochromatographic Assay for the Ultrasensitive and Simultaneous Detection of Bacteria.

Immunochromatographic assays (ICAs) provide simple and rapid strategies for bacterial diagnosis but still suffer from the problems of low sensitivity and high dependency on paired antibodies. Herein, the broad-spectrum capture and detection capability of the antibody-free electropositive nanoprobe are clarified for bacteria for the first time and an ultrasensitive fluorescent ICA platform is constructed for the simultaneous diagnosis of multiple pathogens. A magnetic multilayer quantum dot nanocomposite with an amino-embedded SiO2 shell (MagMQD@Si+) is designed to enrich bacteria from solutions effectively, offer high luminescence, and reduce background signals on test strips, thus greatly improving the sensitivity and stability of ICA technique for pathogen. The superior performance of the MagMQD@Si+-based ICA through the multiplex detection of three common pathogens is demonstrated, namely, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Streptococcus typhi, showing that this ICA possesses high sensitivity (8-40 cells mL-1), good reproducibility (relative standard deviation <5.4%), and high specificity for the three target bacteria. The clinical utility of the proposed method is verified through the detection of 30 real sputum samples from patients with bacterial respiratory infections, revealing that the MagMQD@Si+-based ICA has massive potential as a powerful inspection tool for the rapid, sensitive, and ultrasensitive diagnosis of bacterial infections.

Dynamics of operator size distribution in q-local quantum Brownian SYK and spin model

Dynamics of operator size distribution in q-local quantum Brownian SYK and spin model

Magnetization nutation in magnetic semiconductors: Effective spin model with anisotropic RKKY exchange interaction

Magnetization nutation in magnetic semiconductors: Effective spin model with anisotropic RKKY exchange interaction

Janus graphene nanoribbons with localized states on a single zigzag edge.

Topological design of π electrons in zigzag-edged graphene nanoribbons (ZGNRs) leads to a wealth of magnetic quantum phenomena and exotic quantum phases1-10. Symmetric ZGNRs typically show antiferromagnetically coupled spin-ordered edge states1,2. Eliminating cross-edge magnetic coupling in ZGNRs not only enables the realization of a class of ferromagnetic quantum spin chains11, enabling the exploration of quantum spin physics and entanglement of multiple qubits in the one-dimensional limit3,12, but also establishes a long-sought-after carbon-based ferromagnetic transport channel, pivotal for ultimate scaling of GNR-based quantum electronics1-3,9,13. Here we report a general approach for designing and fabricating such ferromagnetic GNRs in the form of Janus GNRs (JGNRs) with two distinct edge configurations. Guided by Lieb's theorem and topological classification theory14-16, we devised two JGNRs by asymmetrically introducing a topological defect array of benzene motifs to one zigzag edge, while keeping the opposing zigzag edge unchanged. This breaks the structural symmetry and creates a sublattice imbalance within each unit cell, initiating a spin-symmetry breaking. Three Z-shaped precursors are designed to fabricate one parent ZGNR and two JGNRs with an optimal lattice spacing of the defect array for a complete quench of the magnetic edge states at the 'defective' edge. Characterization by scanning probe microscopy and spectroscopy and first-principles density functional theory confirms the successful fabrication of JGNRs with a ferromagnetic ground-state localized along the pristine zigzag edge.

Strong signature of right-handed circularly polarized photoionization close to the cyclotron line in the atmosphere of magnetic white dwarfs

Magnetic fields break the symmetry of the interaction of atoms with photons with different polarizations, yielding chirality and anisotropy properties. The dependence of the absorption spectrum on the polarization, a phenomenon known as dichroism, is present in the atmosphere of magnetic white dwarfs. Its evaluation for processes in the continuum spectrum has been elusive so far due to the absence of appropriate ionization equilibrium models and incomplete data on photoionization cross sections. We combined rigorous solutions to the equilibrium of atomic populations with approximate cross sections to calculate the absolute opacity due to photoionization in a magnetized hydrogen gas. We predict a strong right-handed circularly polarized absorption (χ+) formed blueward of the cyclotron resonance for fields from about 14 to several hundred megagauss. In energies lower than the cyclotron fundamental, this absorption shows a deep trough with respect to linear and left-handed circular polarizations that steepens with the field strength. The jump in χ+ is due to the confluence of a large number of photoionization continua produced by right-handed circularly polarized transitions from atomic states with a nonnegative magnetic quantum number toward different Landau levels.

The Pauli-Poisson equation and its semiclassical limit

. The Pauli-Poisson equation is a semi-relativistic model for charged spin-1∕2-par-ticles in a strong external magnetic field and a self-consistent electric potential computed from the Poisson equation in three space dimensions. It is a system of two magnetic Schrödinger equations for the two components of the Pauli 2-spinor, representing the two spin states of a fermion, coupled by the additional Stern-Gerlach term representing the interaction of magnetic field and spin. We study the global well-posedness in the energy space and the semiclassical limit of the Pauli-Poisson to the magnetic Vlasov-Poisson equation with Lorentz force and the semiclassical limit of the linear Pauli equation to the magnetic Vlasov equation with Lorentz force. We use Wigner transforms and a density matrix formulation for mixed states, extending the work of P. L. Lions & T. Paul as well as P. Markowich & N.J. Mauser on the semiclassical limit of the non-relativistic Schrödinger-Poisson equation.

The Nordic-walking mechanism and its explanation of deconfined pseudocriticality from Wess-Zumino-Witten theory

The understanding of phenomena falling outside the Ginzburg-Landau paradigm of phase transitions represents a key challenge in condensed matter physics. A famous class of examples is constituted by the putative deconfined quantum critical points between two symmetry-broken phases in layered quantum magnets, such as pressurised SrCu2(BO3)2. Experiments find a weak first-order transition, which simulations of relevant microscopic models can reproduce. The origin of this behaviour has been a matter of considerable debate for several years. In this work, we demonstrate that the nature of the deconfined quantum critical point can be best understood in terms of a novel dynamical mechanism, termed Nordic walking. Nordic walking denotes a renormalisation group flow arising from a beta function that is flat over a range of couplings. This gives rise to a logarithmic flow that is faster than the well-known walking behaviour, associated with the annihilation and complexification of fixed points, but still significantly slower than the generic running of couplings. The Nordic-walking mechanism can thus explain weak first-order transitions, but may also play a role in high-energy physics, where it could solve hierarchy problems. We analyse the Wess-Zumino-Witten field theory pertinent to deconfined quantum critical points with a topological term in 2+1 dimensions. To this end, we construct an advanced functional renormalisation group approach based on higher-order regulators. We thereby calculate the beta function directly in 2+1 dimensions and provide evidence for Nordic walking.

Recent Progress on Ultracold-atom Quantum Simulation of Fermi-Hubbard model

Fermi-Hubbard model is a fundamental lattice model for describing correlated electron systems in condensed matter physics, with a profound connection to high-temperature superconductivity. In recent years, quantum simulation with cold atoms has emerged as an important paradigm for studying the Fermi-Hubbard model, while advancements in quantum many-body computations have contributed to our understanding of its fundamental properties. Notably, a recent ultracold-atom experiment achieved the celebrated antiferromagnetic (AFM) phase transition in the three-dimensional (3D) Hubbard model, representing a crucial step in quantum simulation that establishes a foundation for exploring the connection between the quantum magnetism and high-temperature superconductivity. This paper reviews both the experimental and theoretical progress in studying the Fermi-Hubbard model, focusing primarily on 3D systems, discusses the history and current state of developments, and outlines future directions in this field.&lt;br&gt;The paper is organized as follows. We begin with a review of recent progress in observing AFM phase transitions in the 3D Hubbard model, focusing on an ultracold-atom experiment conducted by the research group at the University of Science and Technology of China (USTC). Next, we provide a theoretical introduction to the fundamental properties of the 3D Hubbard model. This includes a summary of prior theoretical studies, an overview of the current research landscape, and a discussion of unresolved or under-explored issues. In the third section, we discuss the quantum simulation of the Hubbard model using ultracold atoms in optical lattices, outlining the basic principle, historical developments and key challenges. The USTC team overcame these challenges with innovative techniques such as atom cooling, large-scale uniform box traps, and precise measurements of the AFM structure factor. Their work successfully confirmed the AFM phase transition via the critical scaling analysis. Finally, we highlight the significance of this achievement and discuss future research prospects for the 3D Hubbard model, including experimental studies on the doped regime and related theoretical benchmarks.

Markov spin models for image generation: explicit large deviations with respect to the number of pixels

Markov spin models for image generation: explicit large deviations with respect to the number of pixels

Explicit symmetry breaking and effective spin models for four-component interacting Fermi gases in lattice potentials

We study low-temperature properties of the four-component Fermi gas of neutral atoms in optical lattice for several cases of explicit breaking of the SU(4) pseudospin symmetry in the framework of the Fermi–Hubbard model. For a reduced two-site system, we analyze the energy states and effective magnetic couplings in cases, where four interacting spin flavors in the Hubbard Hamiltonian form the symmetry subgroups of the type “three by one” or “two by two” according to their tunneling and interaction amplitudes, independently, and study behavior of the corresponding effective Heisenberg models in the limit of strong interaction. We also obtain and analyze the spatial density distributions of spin components in a harmonic optical trap for each case of explicit symmetry breaking.

Dynamics of ferrimagnetic domain wall driven by oscillating magnetic field

Ferrimagnetic materials exhibit ultrafast dynamics similar to those of antiferromagnetic materials near the angular momentum compensation point, where a non-zero net spin density is maintained. This unique feature allows their magnetic structures to be detected and manipulated using traditional magnetic techniques, positioning ferrimagnetic materials as promising candidates for next-generation high-performance spintronic devices. However, effectively controlling the dynamics of ferrimagnetic domain walls remains a significant challenge in current spintronics research.&lt;br&gt;In this work, based on the classic Heisenberg spin model, we employ Landau-Lifshitz-Gilbert (LLG) simulations to investigate the dynamic behavior of ferrimagnetic domain walls driven by sinusoidal and square wave periodic magnetic fields. The results reveal that these two types of oscillating magnetic fields induce distinct domain wall motion modes. Specifically, the domain wall surface, which has non-zero net spin angular momentum, oscillates in response to the external magnetic field. We find that the domain wall velocity decreases as the net spin angular momentum increases. Moreover, the displacement of the ferrimagnetic domain wall driven by a sinusoidal magnetic field increases monotonically with time, while the displacement driven by a square wave magnetic field follows a more tortuous trajectory over time. Under high-frequency field conditions, the domain wall displacement shows more pronounced linear growth, and the domain wall surface rotates linearly with time.This study also explores how material parameters, such as net spin angular momentum, anisotropy, and the damping coefficient, influence domain wall dynamics. Specifically, increasing the anisotropy parameter (&lt;i&gt;d&lt;sub&gt;z&lt;/sub&gt;&lt;/i&gt;) or the damping coefficient (&lt;i&gt;α&lt;/i&gt;) results in a reduction of domain wall velocity. Furthermore, the study demonstrates that, compared to square wave magnetic fields, sinusoidal magnetic fields drive the domain wall more efficiently, leading to faster domain wall motion. By adjusting the frequency and waveform of the periodic magnetic field, the movement of ferrimagnetic domain walls can be precisely controlled, enabling fine-tuned regulation of both domain wall velocity and position.&lt;br&gt;Our findings show that sinusoidal magnetic fields, even at the same intensity, offer higher driving efficiency. The underlying physical mechanisms are discussed in detail, providing valuable insights that can guide the design and experimental development of domain wall-based spintronic devices.

One-third magnetization plateau in Quantum Kagome antiferromagnet

The emergence of nontrivial quantum states from competing interactions is a central issue in quantum magnetism. In particular, for the realization of the quantum spin-liquid state, extensive studies have been conducted on frustrated systems, such as kagome antiferromagnets and Kitaev magnets. Novel quantum states in magnetic fields have remained elusive despite the prediction of rich physics. This can be attributed to material scarcity and the difficulty of precise measurements under ultra-high magnetic fields. Here, in this study, we develop the Kapellasite-type compound InCu3(OH)6Cl3, whose exchange interactions are in appropriate energy scale to comprehensively elucidate the magnetic properties of the frustrated S = 1/2 kagome antiferromagnet. The one-third magnetization plateau was clearly observed. Moreover, the large temperature-linear term in the heat capacity was observed in the magnetic fields, indicating the excitation of gapless quasiparticles in the vicinity of the plateau. These results shed light on the critical behaviors between quantum spin-liquid and -solid in kagome antiferromagnets under high magnetic fields.

Construction of colorimetric-fluorescent dual-signal aptamer-based assay using COF-Au nanozyme and magnetic nanoparticle-based CdTe quantum dots for sensitive zearalenone determination.

Adual-signal aptamer-based assay utilizing colorimetric and fluorescence techniques was developed for the determination of zearalenone (ZEN). The CdTe quantum dots, serving as the fluorescent signal source, were surface-modified onto Fe3O4@SiO2 and subsequently functionalized with the aptamer. The COF-Au was modified with complementary chain, which possessed peroxide (POD)-like enzyme properties, and could catalyze the peroxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to ox TMB, resulting in the generation of colorimetric signals. The two parts were merged based on the principle of base complementary pairing, resulting in an assembled structure exhibiting a diminished fluorescence signal due to the Förster resonance energy transfer (FRET) effect. Due to the higher affinity of the aptamer towards the target, the presence of ZEN resulted in the detachment of COF-Au, leading to an increase in supernatant concentration of COF-Au proportional to ZEN concentration. Consequently, this enhanced thecatalytic ability and amplified thecolorimetric signal. The fluorescence of precipitation increased simultaneously with the reduction of FRET, enabling linear detection of colorimetry in the range 0.5 ~ 10,000μg·kg-1 and fluorescence in the range 0.1 ~ 10,000μg·kg-1, with respective detection limits of 0.36μg·kg-1 and 0.09μg·kg-1. The spike recovery in wheat flour and corn ranged from 93.4 to122.0%. This technology was simple to operate and had low cost and good application prospects.

THE INTERSUBBAND OPTICAL ABSORPTION COEFFICIENT OF THE QD WITH ACCEPTOR IMPURITY UNDER APPLIED ELECTRIC FIELD

In this work, a spherical quantum dot (QD) under the influence of an external electric field is investigated. A multi-band model of the valence band is applied. The influence of off-center acceptor impurity, electric field and QD size dispersion on the absorption coefficient during intersubband transitions between hole states has been analyzed. The results show that an electric field combined with an off-center impurity induces the appearance of two distinct absorption bands corresponding to different magnetic quantum numbers. The intensity of absorption bands depends on the direction and strength of the electric field, and significant differences are observed between fields of opposite polarity. It is important to note that there is a critical field strength that restores the degeneracy of the energy levels, narrowing the broadband absorption tail for systems with small or large dispersion sizes. This research aims to improve the understanding and optimization of the optical properties of nanomaterials.

Frustrated Magnetism and Spin Anisotropy in a Buckled Square Net YbTaO4.

The interplay between quantum effects from magnetic frustration, low-dimensionality, spin-orbit coupling, and crystal electric field in rare-earth materials leads to nontrivial ground states with unusual magnetic excitations. Here, we investigate YbTaO4, which hosts a buckled square net of Yb3+ ions with Jeff = 1/2 moments. The observed Curie-Weiss temperature is about -1 K, implying an antiferromagnetic coupling between the Yb3+ moments. The heat capacity shows no long-range ordering down to 0.10 K, instead shows a field-dependent broad maximum indicative of short-range correlations. The magnetic entropy recovered and magnetization measurements confirm a spin-orbit driven Jeff = 1/2 Kramers doublet ground state. Point charge calculations show that the Yb3+ ions do not host the quintessential XY spin anisotropy observed in typical Yb-based quantum magnets like NaYbO2, YbMgGaO4, and pyrochlores but rather exhibit an almond-shaped anisotropy with an easy axis. Thus, YbTaO4 can serve as a model system to study frustrated magnetism in a square lattice using the J1-J2 Heisenberg model. This work also emphasizes the significance of small perturbations to the local crystal electric field that can alter the spin anisotropy and change the collective behavior of the system.

Resonant Quantum Magnetodielectric Effect in Multiferroic Metal-Organic Framework [CH3NH3]Co(HCOO)3.

The observation of both resonant quantum tunneling of magnetization (RQTM) and resonant quantum magnetodielectric (RQMD) effect in the perovskite multiferroic metal-organic framework [CH3NH3]Co(HCOO)3.is reported. An intrinsic magnetic phase separation emerges at low temperatures due to the hydrogen-bond-modified long-range super-exchange interaction, leading to the coexistence of canted antiferromagnetic order and single-ion (Co2+) magnets. Subsequently, a stair-shaped magnetic hysteresis loop along the [101] direction characterizing the RQTM appears below the magnetic blocking temperature. More interestingly, the magnetic field dependence of dielectric permittivity exhibits pronounced peaks at the critical fields corresponding to the RQTM, a phenomenon termed the RQMD effect which enables electrical detection of the RQTM. The magnetostriction shows a similar behavior to the magnetodielectric effect at 2 and 5 K, which suggests that the magnetodielectric effect in this multiferroic metal-organic framework is related to the spin-lattice coupling.

Coupling Multi‐Space Topologies in 2D Ferromagnetic Lattice

AbstractTopology can manifest topological magnetism (e.g., skyrmion and bimeron) in real space and quantum anomalous Hall (QAH) state in momentum space, which has changed the modern conceptions of matter phase. While the topologies in different spaces are widely studied separately, their coexistence and coupling in a single phase are seldom explored. Here, a novel phenomenon is reported that arises from the interaction of topological magnetism and band topology, the multi‐space topology, in 2D ferromagnetic lattice. Based on continuum theory and tight‐binding model, it is revealed that the interconnection between skyrmion/bimeron and QAH state generates distinctive localized chiral bound states (CBSs). With moderating topological magnetism through a magnetic field, the multi‐space topologies accompanied with different CBSs can be reversed, facilitating the coupling of multi‐space topologies. By performing first‐principles and atomic spin model simulations, such multi‐space topologies and their coupling in monolayer Cr2NSb are further demonstrated. These results represent an important step toward the development of multi‐space topological phenomena in 2D lattice.

Striking Impact of Solvent Polarity on the Strength of Hydrogen-Bonded Complexes: A Nexus Between Theory and Experiment.

The binding free energy of hydrogen-bonded complexes is generally inversely proportional to the solvent dielectric constant. This occurs because the solvent-accessible surface area of the complex is always smaller than that of the individual subsystems, leading to a reduction in solvation energy. The present study explores the potential for stabilizing hydrogen-bonded complexes in a solvent with higher polarity. Contrary to the established understanding, we have demonstrated that the hydrogen-bonded complex (CH3CH2COOH⋅⋅⋅2,4,6-trimethylpyridine) can be better stabilized in a solvent with higher polarity. In this case, a significant charge transfer between the subsystems results in an increased dipole moment of the complex, leading to its stabilization in a more polar solvent. The expected inverse relationship between binding free energy and solvent dielectric constant is observed when the charge transfer between the subsystems is low. Thus, the magnitude of the charge transfer between subsystems is possibly the key factor in determining the stabilization or destabilization of H-bonded complexes in different solvents. Here, we present a comprehensive study that combines experimental and theoretical approaches, including nuclear magnetic resonance (NMR), infrared (IR) spectroscopies and quantum chemical calculations to validate the findings.

Assembling the Puzzle of Coparsite Polymorphism: Synthesis, Thermal Expansion, and Quantum Magnetism of α- and β-Cu4O2(VO4)Cl.

Two new dimorphic spin-1/2 quantum magnets, α- and β-Cu4O2(VO4)Cl, were synthesized via a chemical vapor transport method that emulates mineral formation in volcanic fumaroles. α-Cu4O2(VO4)Cl (1) is a pure vanadate analogue of the coparsite mineral characterized by [O2Cu4]4+ 1D single rods, whereas β-Cu4O2(VO4)Cl (2) adopts a new structure type with the [O2Cu4]4+ 2D layered topology. The thermal expansions of both 1 and 2 studied by high-temperature single-crystal X-ray diffraction are reported. Using ab initio calculations, we infer the presence of antiferromagnetic Cu1-Cu3 units with strong couplings on the order of 200-400 K forming chains (1) and layers (2). The Cu2 atoms are weakly coupled to such units. Magnetic susceptibility measurements corroborate this scenario by showing deviations from the paramagnetic behavior even at 300 K. Moreover, 1 reveals an antiferromagnetic ordering below TN = 24 K with a weak uncompensated magnetic moment.

On the formation and propagation of dust acoustic shock waves in a magnetic quantum dusty plasma

On the formation and propagation of dust acoustic shock waves in a magnetic quantum dusty plasma