Anisotropic Chain Research Articles

Charge Inversion and Ion−Ion Correlation Effects at the Mercury/Aqueous MgSO4 Interface: Toward the Solution of a Long-Standing Issue

Charge inversion is the phenomenon in which an electric double layer contains more counterions than needed to compensate the surface charge. For colloidal particles this has the consequence that the apparent surface charge, as inferred from electrophoresis or interaction studies, has a sign opposite to that of the actual surface charge, obtainable by titration. This phenomenon has been known for over a century. According to the traditional interpretation, the inversion is caused by (chemical) specific adsorption of ions. However, beginning in the early 1980s it has been predicted by a large number of workers that charge inversion should occur as a consequence of many-body ion−ion correlations. For surfaces of sufficiently high surface charge density in the presence of divalent or multivalent counterions, charge inversion is expected to be ubiquitous even in the absence of specific adsorption. Testing this prediction has proved difficult because chemical specific adsorption is a very common phenomenon and can outweigh the effects of ion correlations. So far, no experimental systems have been thoroughly investigated where strong specific adsorption could be unambiguously ruled out under conditions where charge inversion due to ion−ion correlations is predicted. Here, we solve this problem by studying the mercury/aqueous MgSO4 interface. This system has the advantage that highly accurate double layer data are available for a variety of conditions, including some where chemical specific adsorption is known to be absent (or at least very weak). From precise data for this system [Harrison, J. A.; Randles, J. E. B.; Schiffrin, D. J. J. Electroanal. Chem. 1970, 25, 197] one can establish the ionic components of charge and surface charge density. To extract quantitative theoretical predictions about the consequences of ion−ion correlations, we use the highly accurate anisotropic hypernetted chain (AHNC) method, where ion−ion correlations in the double layer are taken into account in a fully self-consistent fashion. It is found that for moderate to large negative surface charge densities and not too high concentration, the variation in the ionic components of charge with the surface charge density can to a large extent be quantitatively explained by enrichment of ions close to the surface due to ion−ion correlations. That chemical specific adsorption of Mg2+ is negligible is supported by considering the properties of the double layer close to the electrocapillary maximum. In view of the large body of evidence indicating that the counterions tend to specifically adsorb on the mercury surface for positive polarization but not for negative, the agreement between theory and experiment for negative surface charge constitutes strong evidence for ion−ion correlations as the origin of charge inversion.

Reversal of thermal rectification in quantum systems

We study thermal transport in anisotropic Heisenberg spin chains using the quantum master equation. It is found that thermal rectification changes sign when the external homogeneous magnetic field is varied. This reversal also occurs when the magnetic field becomes inhomogeneous. Moreover, we can tune the reversal of rectification by temperatures of the heat baths, the anisotropy, and size of the spin chains.

Entanglement creation and storage in two qubits coupling to an anisotropic Heisenberg spin chain

The time evolution of the entanglement of a pair of two spin qubits is investigated when the two qubits simultaneously couple to an environment of an anisotropic Heisenberg XXZ spin chain. The entanglement of the two spin qubits can be created and is a periodic function of the time if the magnetic field is greater than a critical value. If the two spin qubits are in the Bell state, the entanglement can be stored with relatively large value even when the magnetic field is large.

Kink solutions of the classical anisotropic XY chain

We investigate the classical XY model, which is a lattice differential equation on the one-dimensional integer lattice. Depending on an anisotropy parameter γ and an external transverse field of strength λ , we prove the existence of stationary and travelling wave kink solutions.

Effects of Anisotropy on Entanglement in a Two-Qubit Heisenberg XYZ Chain with Intrinsic Decoherence

Taking the intrinsic decoherence effect into account, the entanglement of a two-qubit anisotropic Heisenberg XYZ chain in the presence of the Dzyaloshinski–Moriya (DM) anisotropic antisymetric interaction is investigated in this paper. Concurrence, the measurement of entanglement, is calculated. Compared with the anisotropic in XY plane, the DM interaction is another kind of anisotropic antisymmetric exchange interaction. It is shown that the intrinsic decoherence obviously suppresses the time evolution of the entanglement. The DM interaction only acts on the time evolution of the entanglement when the initial state is |ψ(0)⟩ = cosα|01⟩ + sinα|10⟩ and weakens the degree of entanglement. The anisotropic in XY plane merely impacts on the time evolution of the entanglement when the system is initially in a state |ψ(0)⟩ = cosα|00⟩ +sinα|11⟩. The sufficiently weak anisotropic in XY plane can effectively enhance the degree of entanglement.

Adiabatic dynamics in a spin-1 chain with uniaxial single-spin anisotropy

We study the adiabatic quantum dynamics of an anisotropic spin-1XY chain across a second-order quantum phase transition. The system is driven out ofequilibrium by performing a quench on the uniaxial single-spin anisotropy, that issupposed to vary linearly in time. We show that, for sufficiently large systemsizes, the excess energy after the quench admits a non-trivial scaling behaviorthat is not predictable by standard Kibble–Zurek arguments for isolated criticalpoints or extended critical regions. This emerges from a competing effect of manyaccessible low-lying excited states, inside the whole continuous line of critical points.

Thermal Entanglement in Anisotropic Heisenberg XYZ Chain with External Magnetic Field at Any Finite T

The thermal entanglement of a Two-qubit anisotropic Heisenberg XYZ chain in thermal equilibrium at temperature T in the presence of external magnetic field is investigated, the combined influence of anisotropic interaction and the inhomogeneous magnetic field on the thermal entanglement of the system is examined. Our results show that, the thermal entanglement can be produced at any finite T by adjusting the magnetic field strength, and the critical magnetic field e for which the concurrence C vanishes is increased by introducing the interaction of the z-component of two neighboring spins J z , and by the increasing of the anisotropic parameter γ.

M(N3)2(H2O)2]⋅(bpeado): Unusual Antiferromagnetic Heisenberg Chain (M=Mn) and Ferromagnetic Ising Chain (M=Co) with Large Coercivity and Magnetic Relaxation (bpeado=1,2‐Bis(4‐pyridyl)ethane‐N,N′‐dioxide)

We present here the structures and magnetism of two isostructural magnetic metal-azido chain compounds of the type [M(N(3))(2)(H(2)O)(2)](bpeado) (1, M = Mn; 2, M = Co; bpeado = 1,2-bis(4-pyridyl)ethane-N,N'-dioxide), prepared by utilizing the long spacer bpeado. The structure is composed of [M(N(3))(2)(H(2)O)(2)](n) metal-azido chains, in which metal ions are bridged by two end-on azido ligands, and the chains are further supported by H-bonding interactions between the coordination water of the chain and the lattice bpeado in a three-dimensional (3D) threefold interpenetrated H-bonded framework. Within the structure, the metal-azido chains are separated quite well. Investigation of the magnetic properties has revealed that the Mn compound 1 is an isotropic Heisenberg chain with unusual antiferromagnetic coupling between the Mn(2+) ions linked by double end-on azide anions. The Co compound 2 shows a strong anisotropic Ising-type ferromagnetic chain within the material. Detailed magnetic studies on both polycrystalline and single-crystal samples of 2 have revealed a large coercivity of up to 37.5 kOe (along the crystallographic b-axis), multi-magnetic transitions, and single-chain-magnet-like magnetic relaxation behavior.

Controlling soliton excitations in Heisenberg spin chains through the magic angle

We study the nonlinear dynamics of collective excitation in an N -site XXZ quantum spin chain, which is manipulated by an oblique magnetic field. We show that, when the tilted field is applied along the magic angle, theta_{0}=+/-arccossqrt[13] , the anisotropic Heisenberg spin chain becomes isotropic and thus an freely propagating spin wave is stimulated. Also, in the regime of tilted angles larger and smaller than the magic angle, two types of nonlinear excitations appear: bright and dark solitons.

Suppressed Segmental Relaxation as the Origin of Strain Hardening in Polymer Glasses

A nanometer scale dynamical theory is proposed for the large amplitude strain hardening phenomenon in polymer glasses. The new physical picture is that external deformation induces anisotropic chain conformations, which modifies interchain packing, resulting in density fluctuation suppression and intensification of localizing dynamical constraints and activation barriers. The resulting stresses are of intermolecular origin and arise primarily from prolongation of segmental relaxation, not single chain entropic rubber elasticity. Theoretical predictions for the magnitude, temperature, and deformation rate dependence of the hardening modulus are consistent with experiments and simulations.

Morphology of anisotropic chains in a magneto-rheological fluid during aggregation and disaggregation processes

We study the morphology of the chain-like aggregates formed when a external constant and uniaxial magnetic field is applied to a magneto-rheological (MR) fluid. In order to characterize the conformation of the aggregates, we study the evolution of various fractal dimensions during aggregation and disaggregation processes (i.e., when the applied field is switched on and off), using video-microscopy and image analysis. Experiments have been performed by varying the values of two external parameters: the magnetic field amplitude and particle concentration. We found that the box-counting dimension, related with how the aggregates occupy the surrounding space, depends on the ratio R 1 / R 0 . During the first stage of the disaggregation process, when the particles are moving by Brownian motion inside the aggregate, Family–Vicsek scaling function is verified.

Quantum communication through anisotropic Heisenberg XY spin chains

We study quantum communication through an anisotropic Heisenberg XY chain in a transverse magnetic field. We find that for some time t and anisotropy parameter γ, one can transfer a state with a relatively high fidelity. In the strong-field regime, the anisotropy does not significantly affect the fidelity while in the weak-field regime the affect is quite pronounced. The most interesting case is the intermediate regime where the oscillation of the fidelity with time is low and the high-fidelity peaks are relatively broad. This would, in principle, allow for quantum communication in realistic circumstances. Moreover, we calculate the purity, or tangle, as a measure of the entanglement between one spin and all the other spins in the chain and find that the stronger the anisotropy and exchange interaction, the more entanglement will be generated for a given time.

Force chains in seismogenic faults visualized with photoelastic granular shear experiments

Natural faults have many characteristics in common with granular systems, including granular fault rocks, shear localization, and stick‐slip dynamics. We present experimental results which provide insight into granular behavior in natural faults. The experiments allow us to directly image force chains within a deforming granular media through the use of photoelastic particles. The experimental apparatus consists of a spring‐pulled slider block which deforms the photoelastic granular aggregate at a constant velocity. Particles that carry more of the load appear brighter when viewed through crossed polarizers, making the internal stresses optically accessible. The resulting pattern is a branched, anisotropic force chain network inclined to the shear zone boundaries. Under both constant volume and dilational boundary conditions, deformation occurs predominantly through stick‐slip displacements and corresponding force drops. The particle motion and force chain changes associated with the deformation can either be localized to the central slip zone or span the system. The sizes of the experimental slip events are observed to have power law (Gutenberg‐Richter‐like) distributions; the minimum dimensions of events and the behavior of force chains suggest that a particle scale controls the lower limits of the power law distributions. For large drops in pulling force with slip, the shape of the size distributions is strongly affected by the choice of boundary condition, while for small to moderate drops the probability distributions are approximately independent of boundary condition. These size‐dependent variations in stick‐slip behavior are associated with different spatial patterns: on average, small events typically correspond to localized force chain or particle rearrangements, whereas large events correspond to system‐spanning changes. Such force chain behavior may be responsible for similar size‐dependent behaviors of natural faults.

Ion correlation forces between uncharged dielectric walls

The interaction pressure between two uncharged planar walls immersed in various electrolyte solutions containing mono- and/or divalent ions is investigated. The solution is treated as a primitive model electrolyte, and the wall surfaces constitute dielectric discontinuities. Ionic image charge and ion-wall dispersion interactions are included. The interaction parameters are appropriate for hydrocarbon (polystyrene)/water interfaces, and the electrolyte concentrations considered lie between 0.250M and 1.00M. The anisotropic hypernetted chain method is used to self-consistently calculate the ion density profiles and the ion-ion correlation functions in the inhomogeneous electrolyte. Thereby, the effects of image charge interactions and dispersion interactions on the pressure and the electrolyte structure are included in a fully consistent manner. The explicit consideration of correlations between the ions in the presence of image charges ensures that the screening of the zero-frequency van der Waals interaction is taken into account. Of special interest are the effects of asymmetries between anions and cations with respect to valency and/or dispersion interaction with the walls. Such asymmetries create an electric double layer in the electrolyte outside each electroneutral surface. This causes the wall-wall interaction for large surface separations to be similar to the interaction between charged surfaces. For intermediate separations, around 1-2 nm, a substantial repulsive peak appears in the ionic pressure. In some cases the repulsion is larger than the van der Waals attraction between the walls, which implies that there is a repulsive barrier in the total pressure despite that the surfaces are uncharged. The strongest repulsion is found for 2:1 electrolytes where the monovalent anions interact strongly with the walls via dispersion forces. In general, ion-wall dispersion forces acting on ions of lower valency have a much greater effect than equally strong dispersion forces acting on ions of higher valency. This is mainly due to the more strongly repulsive image charge forces on ions of higher valency that counteract the attractive dispersion forces. Effects of confinement on the ion-ion correlations also contribute to this difference. For all electrolytes the interaction pressure from the ions is attractive for small surface separations. The main cause is a depletion of ions between the walls from the self-image repulsion and confinement effects. For totally symmetric electrolytes the attractive pressure extends to large separations in most cases.

Rotating Fullerene Chains in Carbon Nanopeapods

The rotation of fullerene chains in SWNT peapods is studied using low-voltage high resolution transmission electron microscopy. Anisotropic fullerene chain structures (i.e., C300) are formed in situ in carbon nanopeapods via electron beam induced coalescence of individual fullerenes (i.e., C60). A low electron accelerating voltage of 80 kV is used to prevent damage to the SWNT. The large asymmetric C300 fullerene structure exhibits translational motion inside the SWNT and unique corkscrew like rotation motion. Another asymmetric fullerene chain containing mixed fullerene species is prepared by fusing smaller C60 fullerenes to a larger Sc@C82 fullerene, and this also exhibits corkscrew rotational motion. Chains of Sc3C2@C80 in SWNT peapods adopt a zigzag packing structure, and the entire zigzag chain rotates inside the SWNT to induce structural modifications to the SWNT diameter and cross-sectional shape of the SWNT. The expansion and contraction of the diameter of the SWNT is measured as 17%, demonstrating nanoactuation behavior in carbon nanopeapods.

Polymerization‐direction‐controlled growth of polydiacetylene on artificial silicon oxide templates

AbstractThe control of anisotropic polydiacetylene film formation has been demonstrated on a silicon oxide surface with artificial periodic grooves. A diacetylene monomer film was grown by molecular deposition on the grooves, and polymerization was induced by ultraviolet light irradiation. Anisotropic polymer chain formation was successfully investigated on grooves with a depth larger than 40 nm and a pitch narrower than 2 µm. The interplay between molecular kinetic growth parameters and preferential interaction with a patterned surface has been discussed considering the calculated dimerization energy of monomers. Copyright © 2008 John Wiley & Sons, Ltd.

Soliton spin excitations and their perturbation in a generalized inhomogeneous Heisenberg ferromagnet

We investigate the nonlinear spin dynamics of a generalized inhomogeneous anisotropic Heisenberg ferromagnetic spin chain with bilinear and biquadratic exchange, octupole-dipole, and weak interactions in the semiclassical limit by using Glauber's coherent state method in combination with Holstein-Primakoff bosonic representation of spin operators. The dynamics is found to be governed by a generalized nonlinear Schroedinger equation in the continuum limit. We have identified several completely integrable spin models with soliton spin excitations for specific parametric choices. Finally, we carry out a multiple scale perturbation analysis to find the effect of discreteness and inhomogeneity on the soliton excitations in a more general case. The results show that the discreteness effect introduces symmetric fluctuations in the localized region of the soliton without altering its amplitude and velocity. On the other hand, the inhomogeneity introduces asymmetric fluctuations in the localized region with a decrease in the amplitude and velocity of the soliton with time. Further, the inhomogeneity reverses the velocity of the soliton after some time.

Quantum Chernoff bound metric for theXYmodel at finite temperature

We explore the finite-temperature phase diagram of the anisotropic XY spin chain using the quantum Chernoff bound metric on thermal states. The analysis of the metric elements allows one to easily identify, in terms of different scaling with temperature, quasiclassical and quantum-critical regions. These results extend recent ones obtained using the Bures metric and show that different information-theoretic notions of distance can carry the same sophisticated information about the phase diagram of an interacting many-body system featuring quantum-critical points.

Entanglement of a two-qubit anisotropic Heisenberg XYZ chain in nonuniform magnetic fields with intrinsic decoherence

Taking the intrinsic decoherence effect into account, this paper investigates the entanglement of a two-qubit anisotropic Heisenberg XYZ model in the presence of nonuniform external magnetic fields by employing the concurrence as entanglement measure. It is found that both the intrinsic decoherence and the anisotropy of the system give a significant suppression to the entanglement. Moreover it finds that the initial state of the system plays an important role in the time evolution of the entanglement, which means that the entanglement of the system is independent of the nonuniformity and uniformity of the magnetic field when the system is in the initial state |(0)ψ = |00〉 and | ψ′ (0)〉 = m |01〉 + n |10〉, respectively.

ENHANCED TELEPORTATION THROUGH ANISOTROPIC HEISENBERG QUANTUM SPIN CHAINS

The teleportation via the channel of the thermal equilibrium states in anisotropic Heisenberg XYZ chains is analyzed. It is found that there are the critical temperatures below which entanglement teleportation can be realized. Entanglement teleportation is enhanced through anisotropic XYZ chains in contrast to the isotropic Heisenberg one. Anisotropic spin exchanges can increase these critical temperatures for the teleportation. Entanglement can be transferred in the ferromagnetic anisotropic Heisenberg chain while it cannot be done in the ferromagnetic isotropic one. The average fidelity of the teleportation can be improved in the antiferromagnetic chains.