Spin Model Research Articles

Exotic Synchronization in Continuous Time Crystals Outside the Symmetric Subspace.

Exploring continuous time crystals (CTCs) within the symmetric subspace of spin systems has been a subject of intensive research in recent times. Thus far, the stability of the time-crystal phase outside the symmetric subspace in such spin systems has gone largely unexplored. Here, we investigate the effect of including the asymmetric subspaces on the dynamics of CTCs in a driven dissipative spin model. This results in multistability, and the dynamics becomes dependent on the initial state. Remarkably, this multistability leads to exotic synchronization regimes such as chimera states and cluster synchronization in an ensemble of coupled identical CTCs. Interestingly, it leads to other nonlinear phenomena such as oscillation death and signature of chaos.

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

Double-Q Instability in Noncentrosymmetric Tetragonal Magnets with Bond-Dependent Magnetic Anisotropy Under an In-Plane Magnetic Field

We investigate the instability toward a double-Q state, which consists of a superposition of two spin density waves at different wave vectors, on a two-dimensional noncentrosymmetric square lattice in an in-plane external magnetic field. By performing the simulated annealing for the spin model with the Dzyaloshinskii–Moriya interaction and bond-dependent anisotropic interaction, we obtain four types of double-Q states depending on the sign of the bond-dependent anisotropic interaction. On the other hand, only the single-Q spiral state appears in the absence of the bond-dependent anisotropic interaction. The present results suggest that the interplay between the Dzyaloshinskii–Moriya interaction and bond-dependent anisotropic interaction can give rise to multiple-Q states for both zero and nonzero in-plane magnetic fields.

Role of gaps in the digitized counterdiabatic quantum approximate optimization algorithm for fully connected spin models

Role of gaps in the digitized counterdiabatic quantum approximate optimization algorithm for fully connected spin models

Noise robust detection of quantum phase transitions

Quantum computing allows for the manipulation of highly correlated states whose properties quickly go beyond the capacity of any classical method to calculate. Thus one natural problem which could lend itself to quantum advantage is the study of ground-states of condensed matter models, and the transitions between them. However, current levels of hardware noise can require extensive application of error-mitigation techniques to achieve reliable computations. In this work, we use several IBM devices to explore a finite-size spin model with multiple “phaselike” regions characterized by distinct ground-state configurations. Using preoptimized Variational Quantum Eigensolver (VQE) solutions, we demonstrate that in contrast to calculating the energy, where zero-noise extrapolation is required in order to obtain qualitatively accurate yet still unreliable results, calculations of the energy derivative, two-site spin correlation functions, and the fidelity susceptibility yield accurate behavior across multiple regions, even with minimal or no application of error-mitigation approaches. Taken together, these sets of observables could be used to identify level crossings in a simple, noise-robust manner which is agnostic to the method of ground state preparation. This work shows promising potential for near-term application to identifying quantum phase transitions, including avoided crossings and nonadiabatic conical intersections in electronic structure calculations. Published by the American Physical Society 2024

Local spin-flip transitions induced by magnetic quantum impurities in two-dimensional magnets

Local spin-flip transitions induced by magnetic quantum impurities in two-dimensional magnets

Compass-model physics on the hyperhoneycomb lattice in the extreme spin-orbit regime

The physics of spin-orbit entangled magnetic moments of 4d and 5d transition metal ions on a honeycomb lattice has been much explored in the search for unconventional magnetic orders or quantum spin liquids expected for compass spin models, where different bonds in the lattice favour different orientations for the magnetic moments. Realising such physics with rare-earth ions is a promising route to achieve exotic ground states in the extreme spin-orbit limit; however, this regime has remained experimentally largely unexplored due to major challenges in materials synthesis. Here we report the successful synthesis of powders and single crystals of β-Na2PrO3, with 4f1 Pr4+ jeff = 1/2 magnetic moments arranged on a hyperhoneycomb lattice with the same threefold coordination as the planar honeycomb. We find a strongly non-collinear magnetic order with highly dispersive gapped excitations that we argue arise from frustration between bond-dependent, anisotropic off-diagonal exchanges, a compass quantum spin model not explored experimentally so far. Our results show that rare-earth ions on threefold coordinated lattices offer a platform for the exploration of quantum compass spin models in the extreme spin-orbit regime, with qualitatively distinct physics from that of 4d and 5d Kitaev materials.

Giant Splitting of the Hydrogen Rotational Eigenenergies in the C_{2} Filled Ice.

Hydrogen hydrates exhibit a rich phase diagram influenced by both pressure and temperature, with the so-called C_{2} phase emerging prominently above 2.5GPa. In this phase, hydrogen molecules are densely packed within a cubic icelike lattice and the interaction with the surrounding water molecules profoundly affects their quantum rotational dynamics. Herein, we delve into this intricate interplay by directly solving the Schrödinger's equation for a quantum H_{2} rotor in the C_{2} crystal field at finite temperature, generated through density functional theory. Our calculations reveal a giant energy splitting relative to the magnetic quantum number of ±3.2 meV for l=1. Employing inelastic neutron scattering, we experimentally measure the energy levels of H_{2} within the C_{2} phase at 6.0 and 3.4GPa and low temperatures, finding good agreement with our theoretical predictions. These findings underscore the pivotal role of hydrogen-water interactions in dictating the rotational behavior of the hydrogen molecules within the C_{2} phase and indicate heightened van der Waals interactions compared to other hydrogen hydrates.

Stein’s Method and a Cubic Mean-Field Model

In this paper, we study a mean-field spin model with three- and two-body interactions. In a recent paper (Ann Henri Poincaré, 2024) by Contucci, Mingione and Osabutey, the equilibrium measure for large volumes was shown to have three pure states, two with opposite magnetization and an unpolarized one with zero magnetization, merging at the critical point. The authors proved a central limit theorem for the suitably rescaled magnetization. The aim of our paper is presenting a prove of a central limit theorem for the rescaled magnetization applying the exchangeable pair approach due to Stein. Moreover we prove (non-uniform) Berry–Esseen bounds, a concentration inequality, Cramér-type moderate deviations and a moderate deviations principle for the suitably rescaled magnetization. Interestingly we analyze Berry–Esseen bounds in case the model-parameters (Kn,Jn) converge to the critical point (0, 1) on lines with different slopes and with a certain speed, and obtain new limiting distributions and thresholds for the speed of convergence.

A zero external magnetic field quantum standard of resistance at the 10−9 level

A zero external magnetic field quantum standard of resistance at the 10−9 level

Spiral Spin Liquid in a Frustrated Honeycomb Antiferromagnet: A Single-Crystal Study of GdZnPO.

The frustrated honeycomb spin model can stabilize a subextensively degenerate spiral spin liquid with nontrivial topological excitations and defects, but its material realization remains rare. Here, we report the experimental realization of this model in the structurally disorder-free compound GdZnPO. Using a single-crystal sample, we find that spin-7/2 rare-earth Gd^{3+} ions form a honeycomb lattice with dominant second-nearest-neighbor antiferromagnetic and first-nearest-neighbor ferromagnetic couplings, along with easy-plane single-site anisotropy. This frustrated model stabilizes a unique spiral spin liquid with a degenerate contour around the K{1/3,1/3} point in reciprocal space, consistent with our experiments down to 30mK, including the observation of a giant residual specific heat. Our results establish GdZnPO as an ideal platform for exploring the stability of spiral spin liquids and their novel properties, such as the emergence of low-energy topological defects on the sublattices.

Quantum oscillations in the hole-doped cuprates and the confinement of spinons

A long-standing problem in the study of the under-hole-doped cuprates has been the description of the Fermi surfaces underlying the high magnetic field quantum oscillations, and their connection to the higher temperature pseudogap metal. Harrison and Sebastian [Phys. Rev. Lett. 106, 226402 (2011)] proposed that the pseudogap "Fermi arcs" are reconstructed into an electron pocket by field-induced charge density wave order. But computations on such a model [Zhang and Mei, Europhys. Lett. 114, 47008 (2016)] show an unobserved additional oscillation frequency from a Fermi surface arising from the backsides of the hole pockets completing the Fermi arcs. We describe a transition from a fractionalized Fermi liquid (FL*) model of the pseudogap metal, to a metal with bidirectional charge density wave order without fractionalization. We show that the confinement of the fermionic spinon excitations of the FL* across this transition can eliminate the unobserved oscillation frequency.