Long-range Dipolar Interactions Research Articles

A Voltage-Modulated Nanostrip Spin-Wave Filter and Spin Logic Device Thereof.

A nanostrip magnonic-crystal waveguide with spatially periodic width modulation can serve as a gigahertz-range spin-wave filter. Compared with the regular constant-width nanostrip, the periodic width modulation creates forbidden bands (band gaps) at the Brillouin zone boundaries due to the spin-wave reflection by the periodic potential owing to the long-range dipolar interactions. Previous works have shown that there is a critical challenge in tuning the band structures of the magnonic-crystal waveguide once it is fabricated. In this work, using micromagnetic simulations, we show that voltage-controlled magnetic anisotropy can effectively tune the band structures of a ferromagnetic-dielectric heterostructural magnonic-crystal waveguide. A uniformly applied voltage of 0.1 V/nm can lead to a significant frequency shift of ~9 GHz. A spin-wave transistor prototype employing such a kind of spin-wave filter is proposed to realize various logical operations. Our results could be significant for future magnonic computing applications.

Prethermal nematic order and staircase heating in a driven frustrated Ising magnet with dipolar interactions

Many-body systems subject to a high-frequency drive can show intriguing thermalization behavior. Prior to heating to a featureless infinite-temperature state, these systems can spend an exponentially long time in prethermal phases characterized by various kinds of order. Here, we uncover the rich non-equilibrium phase diagram of a driven frustrated two-dimensional Ising magnet with competing short-range ferromagnetic and long-range dipolar interactions. We show that the ordered stripe and nematic phases, which appear in equilibrium as a function of temperature, underpin subsequent prethermal phases in a new multi-step heating process en route towards the ultimate heat death. We discuss implications for experiments on ferromagnetic thin films and other driving induced phenomena in frustrated magnets.

Spin-ice behavior of mixed pyrochlore Dy2GaSbO7 exhibiting enhanced Pauling zero-point entropy

Herein, the low-temperature magnetothermal properties and spin-ice physics of a mixed pyrochlore, Dy2GaSbO7 (DGS), are investigated through dc magnetization, ac susceptibility, and heat capacity experiments, and crystal-field computation. A Curie-Weiss (CW) fit to the dc susceptibility data yields effective magnetic moment, μeff = 10.0 μB/Dy3+ and CW temperature, θCW = +1.62 K. Magnetization attains a saturation value of Msat = 5.06μB/Dy above H ≈ 8 T and at T = 2 K, which is half of the μeff due to the effective Ising-type anisotropy along local 〈111〉 axes of the elementary Dy4O′ tetrahedron, illustrating DGS as an effective spinS∼ = 1/2 system. The dc susceptibility data are interpreted satisfactorily within the framework of a crystal-field theory and a mean-field approximation taking account of long-range dipolar interactions and anisotropic exchange interactions between the nearest-neighbor Dy3+-ions. AC susceptibility exhibits anomaly at a temperature Tice ≈ 3.13 K at frequency of f = 111 Hz, which is a signature of dynamical freezing of spins into a disordered state in compliance with the spin-ice rules. Heat capacity at zero field also shows a peak at 1.36 K and a low kink at 3.25 K which smears out on application of the magnetic field. The calculated magnetic entropy of DGS at zero field is 2.82 J K−1(mol-Dy)−1, which is much less than the Pauling spin-ice value of 4.1 J K−1mol−1. The spin-ice entropy is restored with a value of 4.50 J K−1(mol-Dy)−1 at a field of 1 T. The zero-point entropy of DGS becomes 2.94 J K−1(mol-Dy)−1 which is larger than Pauling zero-point entropy of 1.686 J K−1mol−1 for cannonical dipolar spin-ice materials, e.g., Dy2Ti2O7 and Ho2Ti2O7. The enhanced entropy of DGS may be induced due to random chemical disorder and varied chemical pressure of B-site (GaSb tetrahedra) ions. Thus, the present study creates a new pathway to extend the horizon of spin-ice physics.

An optical tweezer array of ground-state polar molecules

Fully internal and motional state controlled and individually manipulable polar molecules are desirable for many quantum science applications leveraging the rich state space and intrinsic interactions of molecules. While prior efforts at assembling molecules from their constituent atoms individually trapped in optical tweezers achieved such a goal for exactly one molecule (Zhang J T et al 2020 Phys. Rev. Lett. 124 253401; Cairncross W B et al 2021 Phys. Rev. Lett. 126 123402; He X et al 2020 Science 370 331–5), here we extend the technique to an array of five molecules, unlocking the ability to study molecular interactions. We detail the technical challenges and solutions inherent in scaling this system up. With parallel preparation and control of multiple molecules in hand, this platform now serves as a starting point to harness the vast resources and long-range dipolar interactions of molecules.

Collective States of Active Particles With Elastic Dipolar Interactions

Many types of animal cells exert active, contractile forces and mechanically deform their elastic substrate, to accomplish biological functions such as migration. These substrate deformations provide a mechanism in principle by which cells may sense other cells, leading to long-range mechanical inter–cell interactions and possible self-organization. Here, inspired by cell mechanobiology, we propose an active matter model comprising self-propelling particles that interact at a distance through their mutual deformations of an elastic substrate. By combining a minimal model for the motility of individual particles with a linear elastic model that accounts for substrate-mediated, inter–particle interactions, we examine emergent collective states that result from the interplay of motility and long-range elastic dipolar interactions. In particular, we show that particles self-assemble into flexible, motile chains which can cluster to form diverse larger-scale compact structures with polar order. By computing key structural and dynamical metrics, we distinguish between the collective states at weak and strong elastic interaction strength, as well as at low and high motility. We also show how these states are affected by confinement within a channel geometry–an important characteristic of the complex mechanical micro-environment inhabited by cells. Our model predictions may be generally applicable to active matter with dipolar interactions ranging from biological cells to synthetic colloids endowed with electric or magnetic dipole moments.

Effect of interparticle dipolar interaction on pore clogging during microfiltration.

We present numerical investigations on the clogging of adhesive particles carrying electric dipoles at pore scale using an adhesive discrete element method (DEM). Based on the simulation results, the long-range dipolar interaction is reported to promote the clogging process, which is quantified by the bulk permeability, the penetrating particle number, and the particle capture efficiency. A clogging phase diagram is constructed in terms of the Stokes number (St) and the adhesion parameter (Ad) for both neutral and polarized particles. The influence of the dipolar interaction on the clogging-nonclogging transition is then described by the shifted boundary on the diagram. Also, the cake structure is characterized by different mathematical descriptions. A looser structure is formed with the increase of both the short-range adhesion and the long-range dipolar interaction. More ordered structures, such as particle chains, are observed in the presence of the stronger dipolar interaction. Furthermore, fluid stress is found to be essential in the compression and restructuring of the cake structure. Finally, a schematic representation of the cake structure is established, which provides a general physical picture showing the relationship between the cake structure and the particle-scale interactions.

Anomalous spin waves in CsFeCl3 and RbFeCl3

We investigate magnetic excitations in the $S=1$ easy-plan-type triangular antiferromagnets CsFeCl$_{3}$ and RbFeCl$_{3}$ through a combination of inelastic neutron scattering measurements and spin-wave theory calculations based on an established exchange-coupling Hamiltonian. We show that in either material the model falls short of providing an adequate description of the measured intensities and for RbFeCl$_{3}$ even fails to reproduce the measured dispersion relation. The most striking discrepancy is a very anisotropic azimuthal intensity distribution in the acoustic spin-wave branches in the long-wavelength limit, which is incompatible with spin-wave theory on a fundamental level. The observed anomalies are attributed to long-range dipolar interactions.

Stripe-on-plane-wave phase of a binary dipolar Bose gases with soft-core long-range interactions

Long-range interactions are ubiquitous in nature and are studied in a variety of physical fields. The recent realization of soft-core long-range interaction in ultracold quantum gases broadens the research field of long-range interactions. We consider a binary Bose–Einstein condensate with both long-range dipolar and long-range soft-core interactions. The ground-state phase diagrams of the system have been mapped out in full parameter space accounting for the dipolar and soft-core long-range interactions, as well as the orientation of the dipoles. The results show that the interplay between long-range isotropic and anisotropic interactions results in a variety of ground state phases, such as supersolid, standing wave, and stripe-on-plane-wave phases. In particular, the effects of dipolar and soft-core long-range interaction, together with the orientation of the dipoles, have also been discussed in each ground state phase. The experimental feasibility of the parameters are within the current experimental capacity.

Tuning of dipolar interactions and evaporative cooling in a three-dimensional molecular quantum gas

Ultracold polar molecules possess long-range, anisotropic and tunable dipolar interactions, providing opportunities to probe quantum phenomena that are inaccessible with existing cold gas platforms. However, experimental progress has been hindered by the dominance of two-body loss over elastic interactions, which prevents efficient evaporative cooling. Although recent work has demonstrated controlled interactions by confining molecules to a two-dimensional geometry, a general approach for tuning molecular interactions in a three-dimensional stable system has been lacking. Here we demonstrate tunable elastic dipolar interactions in a bulk gas of ultracold 40K87Rb molecules in three dimensions, facilitated by an electric field-induced shielding resonance that suppresses the reactive loss by a factor of 30. This improvement in the ratio of elastic to inelastic collisions enables direct thermalization. The thermalization rate depends on the angle between the collisional axis and the dipole orientation controlled by an external electric field, a direct manifestation of the anisotropic dipolar interaction. We achieve evaporative cooling mediated by the dipolar interactions in three dimensions. This work demonstrates full control of a long-lived bulk quantum gas system with tunable long-range interactions, paving the way for the study of collective quantum many-body physics. Realizing the potential of dipolar molecular gases to explore quantum physics needs elastic, tunable interactions and low temperatures. This is now possible due to advances in control that suppress molecular losses and enable efficient cooling.

Effect of particle dipolar interactions on the viscoelastic response of dilute ferrofluids undergoing oscillatory shear

In this work, we investigate the viscoelastic behavior of a ferrofluid undergoing an oscillatory simple shear flow and also under the influence of an external magnetic field. The main goal is to examine the influence of the dipolar interactions and formation of anisotropic structures on the macroscopic rheological response of these complex fluids. This study is performed by direct numerical simulation of neutrally buoyant, Brownian magnetic spheres in the limit of vanishingly small Reynolds numbers using Brownian dynamics. The long-range dipolar interactions are computed by the Ewald summation technique. We present the in-phase and out-of-phase rotational viscosity components as a function of the oscillatory frequency for several values of the dipolar interaction parameter and shear strain. The results show that the viscoelastic transition in the fluid is anticipated in the presence of dipolar interactions. These phenomena are probably related to the formation of complex structures in the fluid like anisotropic linear chains. In addition, a qualitative analysis of microstructure transitions during the suspension time evolution indicates the formation of long anisotropic chains for the high strength of the dipolar interaction and small shear rates. The simulation results are compared with the classical Maxwell linear viscoelastic model, and a characteristic relaxation time is identified for the investigated ferrofluid. We also offer evidence that this relaxation time has a quadratic power law scaling dependence on the dipolar interaction parameter and that the dipolar interactions are the main physical mechanics, which creates elastic response of the ferrofluid investigated here as a direct consequence of the gain of memory at the microscopic level due to the action of the magnetic torque on the particles and the formation of oriented aggregative structures like anisotropic chains.

Dipolar Ising model: Phases, growth laws, and universality.

The behavior of many magnetic and dielectric solids, and the more contemporary magnetic superlattices, is governed by dipolar interactions. They are anisotropic and long ranged, having varied consequences ranging from ground states with complicated magnetic order to the presence of glassy dynamics characterized by a plethora of relaxation times. These systems are well captured by the dipolar Ising model (DIM) with nearest-neighbor exchange interactions (J) and long-range dipolar interactions (D). Depending on the relative interaction strength Γ=J/D, there are four phases of distinct magnetic order and symmetry. Using Monte Carlo simulations, we perform deep quenches to study domain growth or coarsening in the d=3 DIM. This important nonequilibrium phenomenon has not been addressed as dipolar interactions are notoriously difficult to handle theoretically. Our study reveals that, in spite of the anisotropy in interactions and diversity in ground state configurations, we observe universality in the ordering dynamics of all phases.

Extreme Ultraviolet Second Harmonic Generation Spectroscopy in a Polar Metal.

The coexistence of ferroelectricity and metallicity seems paradoxical, since the itinerant electrons in metals should screen the long-range dipole interactions necessary for dipole ordering. The recent discovery of the polar metal LiOsO3 was therefore surprising [as discussed earlier in Y. Shi et al., Nat. Mater. 2013, 12, 1024]. It is thought that the coordination preferences of the Li play a key role in stabilizing the LiOsO3 polar metal phase, but an investigation from the combined viewpoints of core-state specificity and symmetry has yet to be done. Here, we apply the novel technique of extreme ultraviolet second harmonic generation (XUV-SHG) and find a sensitivity to the broken inversion symmetry in the polar metal phase of LiOsO3 with an enhanced feature above the Li K-edge that reflects the degree of Li atom displacement as corroborated by density functional theory calculations. These results pave the way for time-resolved probing of symmetry-breaking structural phase transitions on femtosecond time scales with element specificity.

Quantifying the effects of long-range\xa013C-13C dipolar coupling on measured relaxation rates in RNA

Selective stable isotope labeling has transformed structural and dynamics analysis of RNA by NMR spectroscopy. These methods can remove 13C-13C dipolar couplings that complicate 13C relaxation analyses. While these phenomena are well documented for sites with adjacent 13C nuclei (e.g. ribose C1′), less is known about so-called isolated sites (e.g. adenosine C2). To investigate and quantify the effects of long-range (> 2 Å) 13C-13C dipolar interactions on RNA dynamics, we simulated adenosine C2 relaxation rates in uniformly [U-13C/15N]-ATP or selectively [2-13C]-ATP labeled RNAs. Our simulations predict non-negligible 13C-13C dipolar contributions from adenosine C4, C5, and C6 to C2 longitudinal (R1) relaxation rates in [U-13C/15N]-ATP labeled RNAs. Moreover, these contributions increase at higher magnetic fields and molecular weights to introduce discrepancies that exceed 50%. This will become increasingly important at GHz fields. Experimental R1 measurements in the 61 nucleotide human hepatitis B virus encapsidation signal ε RNA labeled with [U-13C/15N]-ATP or [2-13C]-ATP corroborate these simulations. Thus, in the absence of selectively labeled samples, long-range 13C-13C dipolar contributions must be explicitly taken into account when interpreting adenosine C2 R1 rates in terms of motional models for large RNAs.

Transport and Annihilation of the Triplets in Organic Phosphorescent Systems: Kinetic Monte Carlo Simulation and Modeling

We use kinetic Monte Carlo (kMC) simulations to study transport and annihilation of the triplet excitons in organic phosphorescent host–guest systems. By assuming a short-range hopping mechanism for the triplet transport and a long-range dipolar interaction for the triplet–triplet annihilation (TTA), we examine the effect of the relevant experimental parameters on the decay kinetics of the triplets in an energy-disordered system. It is shown that for the range of parameters typical of the organic host–guest systems, transport of the triplets at room temperature is dispersive during their lifetime, with a dispersion exponent of 0.4 < γ < 0.6. We also provide a quantitative comparison between the kMC simulations and the traditional rate coefficients used to describe the TTA. We then suggest and justify a modified rate coefficient that can explain the TTA for a wide range of the system parameters. As the method of analysis, we focus on (a transformed) probability density function of the triplet decay and show that valuable insights into the statistics of the annihilation and the so-called efficiency roll-off can be obtained using this approach. We also discuss how and when describing the annihilation process in terms of an effective time-independent rate can be used to quantify the TTA in the host–guest systems. The results presented in this work are also relevant for other organic devices in which TTA plays a key role in the performance of the system.

Vortex structure in magnetic nanodots: Dipolar interaction, mobile spin model, phase transition and melting

We study in this article properties of a nanodot embedded in a support by Monte Carlo simulation. The nanodot is a piece of simple cubic lattice where each site is occupied by a mobile Heisenberg spin which can move from one lattice site to another under the effect of the temperature and its interaction with neighbors. We take into account a short-range exchange interaction between spins and a long-range dipolar interaction. We show that the ground-state configuration is a vortex around the dot central axis: the spins on the dot boundary lie in the xy plane but go out of plane with a net perpendicular magnetization at the dot center. Possible applications are discussed. Finite-temperature properties are studied. We show the characteristics of the surface melting and determine the energy, the diffusion coefficient and the layer magnetizations as functions of temperature.

Temperature and thickness dependent magnetization reversal in 2D layered ferromagnetic material Fe3GeTe2

Advance in the field of two-dimensional (2D) Van der Waals layered magnetic materials have made the atomic-thickness spintronic devices possible in the near future. The application of the 2D layered magnetic materials inevitably involves the magnetization reversal. Here we study the magnetization reversal of the 2D layered material Fe3GeTe2 by means of magnetic and anomalous Hall resistance measurements. We find the reversal process of Fe3GeTe2 flake is temperature and thickness dependent. For thin flakes and at low temperatures, the hysteresis loops have perfect rectangular shapes with large coercivity, indicating the single domain characteristic during the reversal process. With increasing temperature, a cross-over from single domain to multi-domain structure occurs. For bulk and very thick flakes Fe3GeTe2, the nearly zero magnetic remanence and small coercivity demonstrates that the reversal process is accomplished through the formation of multi-domain structure and its gradual evolution with the magnetic field. The change of magnetization reversal with temperature and flake thickness is explained based on the competition between the long-range magnetic dipolar interaction and the perpendicular magnetic anisotropy. The results obtained in this work provide important reference for designing Fe3GeTe2-based spintronic devices.

Topological pumping of a 1D dipolar gas into strongly correlated prethermal states.

Long-lived excited states of interacting quantum systems that retain quantum correlations and evade thermalization are of great fundamental interest. We create nonthermal states in a bosonic one-dimensional (1D) quantum gas of dysprosium by stabilizing a super-Tonks-Girardeau gas against collapse and thermalization with repulsive long-range dipolar interactions. Stiffness and energy-per-particle measurements show that the system is dynamically stable regardless of contact interaction strength. This enables us to cycle contact interactions from weakly to strongly repulsive, then strongly attractive, and finally weakly attractive. We show that this cycle is an energy-space topological pump (caused by a quantum holonomy). Iterating this cycle offers an unexplored topological pumping method to create a hierarchy of increasingly excited prethermal states.

Quantum paraelectric state and critical behavior in Sn(Pb)2P2S(Se)6 ferroelectrics

The dipole ordering in Sn(Pb)2P2S(Se)6 materials may be tuned by chemical substitution realizing a ferroelectric quantum phase transition and quantum glassy or relaxor type phenomena on different parts of the phase diagram. The introduction of Ge impurity increases the temperature of the phase transitions and initiates a more pronounced Ising type critical anomaly in the Sn2P2S6 crystal, does not shift the coordinate of the Lifshitz point xLP in Sn2P2(SexS1−x)6 mixed crystals, and induces the appearance of a ferroelectric phase transition in quantum paraelectrics Pb2P2S6 and inhomogeneous polar ordering in (Pb0.7Sn0.3)2P2S(Se)6 crystals. For the Pb2P2S6 crystal, the real part of the dielectric permittivity in the quantum critical regime varies as 1/T2 instead of the expected 1/T3 behavior for uniaxial materials. Such an observation can be partially explained by a screening phenomenon in the semiconductor materials of the Sn(Pb)2P2S(Se)6 system, which weakens the long-range electric dipole interactions, and also provides, at high temperatures, a critical behavior near the Lifshitz point (studied by thermal diffusivity) similar to the one predicted in the case of systems with short-range interactions. At low temperatures, a quantum critical behavior in the Pb2P2S6 crystal can be established by a small amplitude of electric dipoles together with the nonlinear coupling between polar and antipolar fluctuations. An increase in thermal conductivity is induced by Ge impurity in the Pb2P2S6 crystal, which is explained by the weakening of the acoustic phonons resonance scattering by soft optic phonons because of the appearance of ferroelectric phase polar clusters.

Dipolar evaporation of reactive molecules to below the Fermi temperature.

SummaryMolecules are the building blocks of matter and their control is key to the investigation of new quantum phases, where rich degrees of freedom can be used to encode information and strong interactions can be precisely tuned1. Inelastic losses in molecular collisions2–5, however, have greatly hampered the engineering of low-entropy molecular systems6. So far, the only quantum degenerate gas of molecules has been created via association of two highly degenerate atomic gases7,8. Here, we use an external electric field along with optical lattice confinement to create a two-dimensional (2D) Fermi gas of spin-polarized potassium-rubidium (KRb) polar molecules, where elastic, tunable dipolar interactions dominate over all inelastic processes. Direct thermalization among the molecules in the trap leads to efficient dipolar evaporative cooling, yielding a rapid increase in phase-space density. At the onset of quantum degeneracy, we observe the effects of Fermi statistics on the thermodynamics of the molecular gas. These results demonstrate a general strategy for achieving quantum degeneracy in dipolar molecular gases where strong, long-range, and anisotropic dipolar interactions can drive the emergence of exotic many-body phases, such as interlayer pairing and p-wave superfluidity.

Long-Range Interaction Enhanced Adiabatic Quantum ComputersSupported by the National Natural Science Foundation of China (Grant Nos. U1930201, 11574239 and 91836101).

A quantum computer is not necessarily alone, e.g., thousands and millions of quantum computers are simultaneously working together for adiabatic quantum computers based on nuclear spins. Long-range interaction is inevitable between these nuclear spin qubits. Here we investigate the effect of long-range dipolar interaction between different adiabatic quantum computers. Our analytical and numerical results show that the dipolar interaction can enhance the final fidelity in adiabatic quantum computation for solving the factorization problem, when the overall interaction is negative. The enhancement will become more prominent if a single quantum computer encounters an extremely small energy gap which occurs more likely for larger-size systems.