Neighboring Spin Pairs Research Articles

Rate distortion theorem and the multicritical point of a spin glass.

A spin system can be thought of as an information coding system that transfers information of the interaction configuration into information of the equilibrium state of the spin variables. Hence it can be expected that the relations between the interaction configuration and equilibrium states are consistent with the known laws of information theory. We show that Shannon's rate distortion theorem can be used to obtain a universal constraint on neighboring spin correlations for a broad range of Ising spin systems with two-body spin interactions. Remarkably, this constraint gives a bound for the multicritical point in the phase diagram, when a mean-field behavior for the neighboring spin pairs can be expected in the paramagnetic phase.

Wide crossover in the 3D Ashkin–Teller model

The phase transition line, for which the possibility of the non-universal behavior studied by Monte Carlo (MC) simulations had been announced, in the standard 3D Ashkin–Teller (AT) model phase diagram is carefully investigated. The results of our MC experiments for transitions between paramagnetic, mixed, and Baxter phases for negative coupling between neighboring spin pairs, the most complex and least recognized region in the phase diagram, are presented. Binder, Challa, and also for the first time of Lee–Kosterlitz cumulants, the last two adapted to the AT model, are exploited. The uncommon coexistence of continuous and first order phase transitions along the same phase boundary on different components of the order parameter are reported. The paper is closed with the conclusion of a wide crossover effect that covers the whole line between tricritical points, where earlier papers indicate the possibility of non-universal behavior with the critical exponent values varying continuously.

Magnetic quantum correlations in the one-dimensional transverse-field XXZ model

One-dimensional spin-1/2 systems are well-known candidates to study the quantum correlations between particles. In the condensed matter physics, studies often are restricted to the 1st neighbor particles. In this work, we consider the 1D XXZ model in a transverse magnetic field (TF) which is not integrable except at specific points. Analytical expressions for quantum correlations (entanglement and quantum discord) between spin pairs at any distance are obtained for both zero and finite temperature, using an analytical approach proposed by Caux et al. [PRB 68, 134431 (2003)]. We compare the efficiency of the QD with respect to the entanglement in the detection of critical points (CPs) as the neighboring spin pairs go farther than the next nearest neighbors. In the absence of the TF and at zero temperature, we show that the QD for spin pairs farther than the 2nd neighbors is able to capture the critical points while the pairwise entanglement is absent. In contrast to the pairwise entanglement, two-site quantum discord is effectively long-range in the critical regimes where it decays algebraically with the distance between pairs. We also show that the thermal quantum discord between neighbor spins possesses strong distinctive behavior at the critical point that can be seen at finite temperature and, therefore, spotlights the critical point while the entanglement fails in this task.

Entanglement entropy scaling in solid-state spin arrays via capacitance measurements

Solid-state spin arrays are being engineered in varied systems, including gated coupled quantum dots and interacting dopants in semiconductor structures. Beyond quantum computation, these arrays are useful integrated analog simulators for many-body models. As entanglement between individual spins is extremely short ranged in these models, one has to measure the entanglement entropy of a block in order to truly verify their many-body entangled nature. Remarkably, the characteristic scaling of entanglement entropy, predicted by conformal field theory, has never been measured. Here we show that with as few as two replicas of a spin array, and capacitive double-dot singlet-triplet measurements on neighboring spin pairs, the above scaling of the entanglement entropy can be verified. This opens up the controlled simulation of quantum field theories, as we exemplify with uniform chains and Kondo-type impurity models, in engineered solid-state systems. Our procedure remains effective even in the presence of typical imperfections of realistic quantum devices and can be used for thermometry, and to bound entanglement and discord in mixed many-body states.

Exchange kinetics by inversion transfer: integrated analysis of the phosphorus metabolite kinetic exchanges in resting human skeletal muscle at 7 T.

To develop an inversion pulse-based, chemical exchange saturation transfer-like method for detection of (31) P magnetization exchanges among all nuclear magnetic resonance visible metabolites suitable for providing an integrated kinetic analysis of phosphorus exchange reactions in vivo. The exchange kinetics by inversion transfer (EKIT) sequence includes application of a frequency-selective inversion pulse arrayed over the range of relevant (31) P frequencies, followed by a constant delay and a hard readout pulse. A series of EKIT spectra, each given by a plot of Z-magnetization for each metabolite of interest versus frequency of the inversion pulse, can be generated from this single data set. EKIT spectra reflect chemical exchange due to known biochemical reactions, cross-relaxation effects, and relayed magnetization transfers due to both processes. The rate constants derived from EKIT data collected on resting human skeletal muscle were: ATP synthesis via ATP synthase (0.050 ± 0.016 s(-1) ), ATP synthesis via creatine kinase (0.264 ± 0.023 s(-1) ), and cross-relaxation between neighboring spin pairs within ATP (0.164 ± 0.022 s(-1) ). EKIT provides a simple, alternative method to detect chemical exchange, cross relaxation, and relayed magnetization transfer effects in human skeletal muscle at 7 T.

Magnetic dipolar ordering on geometrically frustrated brick-shaped lattices

The magnetic ordering of frustrated arrays of nanoscale islands can be strongly influenced by the array patterns. We theoretically present three kinds of artificial geometrically frustrated systems with different brick-shaped geometries, defined as brick-shaped lattices, and investigate their magnetic dipolar ordering at the ground state using the Monte Carlo method. The simulated results show that the magnetic ordering of three brick-shaped frustrated lattices depends strongly on the strength of dipolar interactions, depending on the lattice spacing. It is found that the long-range dipolar interactions tend to suppress the long-range ordered state and induce the short-range quasi-ice state at each vertex of the lattices. In addition, the correlations for neighboring spin pairs are closely related to not only the dipolar coupling strength but also the geometry of the lattices.

Double-layer antiferromagnetic quantum spin- [formula omitted] Heisenberg model: study of the ground state

The crossover from two-dimensional to three-dimensional behavior in the quasi-two-dimensional quantum Heisenberg antiferromagnetic model in the presence of a magnetic field, at T = 0 (ground state), is studied by using effective-field theory. In the model a nearest neighbour spin pair interacts with strength J in the xy-plane and with λJ ( 0 ⩽ λ ⩽ 1 ) in the z-axis. The critical field H c is obtained as a function of parameter λ, where we have different values of the classical case (Ising model) H c / J = 4 + 2 λ .

Low temperature phase of the quantum triangular lattice XY model with Dzyaloshinsky-Moriya interaction

The critical behaviour and low temperature phase of a generalized XY model with symmetric K and antisymmetric (Dzyaloshinsky-Moriya) D interactions on the triangular lattice is studied. For the quantum s = 1 2 version the finite temperature real space renormalization group method is applied to find the critical lines in the plane ( K, D) and to estimate the nearest neighbour spin pair correlations. For the classical model, using Spin Molecular Dynamics simulations the ground state configurations and stability of an initial in-plane “vortex” are investigated.

Finite-size effects of dimensional crossover in the quasi-two-dimensional three-state Potts model

A nearest neighbour spin pair of the quasi-two-dimensional three-state Potts model interacts with strength J(>0) in the xy-plane and with λJ (0⩽ λ ⪡ 1) on the z-axis. The phase transition is of second-order when λ=0 and is of first-order when λ>0. Dimensional crossover occurs with a change of the order of the phase transition. We study the finite-size effects of the phenomenon by using a Monte Carlo method with a multi-spin coding technique. The prediction of the finite-size scaling theory is consistent with the Monte Carlo results.

Finite-size effects in the quasi-two-dimensional Ising model

Abstract In the quasi-two-dimensional Ising model a nearest neighbour spin pair interacts with strength J (> 0) in the xy-plane and with λJ (0 ≤ λ ⪡ 1) in the z-axis. It shows crossover from two-dimensional to three-dimensional behaviour as the critical point is approached. We study the finite-size effects of the phenomenon by using a Monte Carlo method with the multi-spin coding technique. We derive the finite-size scaling form of the critical temperature defined as the peak position of the specific heat. It is consistent with the Monte Carlo results.

Temperature Dependence of the Absorption Spectra6A1g→4A1g(4G),4Eg(4G) in the Quasi Two-Dimensional Antiferromagnets (CnH2n+1NH3)2MnCl4(n=2, 3)

The absorption spectra corresponding to the transitions 6 A 1g → 4 A 1g ( 4 G ), 4 E g ( 4 G ) in (C n H 2 n +1 NH 3 ) 2 MnCl 4 ( n =2, 3) were measured between liquid helium and room temperatures. The temperature dependence of the integrated intensities of these spectra suggests that magnon assisted electric dipole transitions are dominant in these spectra. The temperature dependence of energies of these absorption spectra is very similar to that of the nearest neighbour spin pair correlation function which reflects mainly the energy of short wave-length magnon.The temperature dependence of the integrated intensities and the energies of these absorption spectra shows the two-dimensional magnetic character.