Thermal entanglement in the Heisenberg XXZ model with Dzyaloshinskii–Moriya interaction

By the concept of negativity, we investigate the thermal entanglement in the two-spin $(\frac{1}{2},s)$ Heisenberg XXX and XXZ models in the presence of Dzyaloshinskii–Moriya $\left(DM\right)$ interactions respectively. Through calculation, we know that for the XXZ model, the $\Delta$ and $s$ can be used together to control the extent of entanglement and, in particular, to obtain large entanglement. The effect of spin in both models shows that it can increase the critical temperature and the negativity decreases as the spin increases. We found that the DM interaction has different effects on Fermi and Bose systems so it can not only excite entanglement but also affect the entanglement in different spin systems.     

Spin and charge Nernst effect in a four-terminal double-dot interferometer

We investigate the spin and charge Nernst effect of a four-terminal Aharonov–Bohm interferometer with Rashba spin–orbit interaction (RSOI). It is shown that a pure spin Nernst effect or a fully spin-polarized Nernst effect can be obtained by modulating the magnetic flux phase ? and the RSOI induced phase φ. It is also demonstrated that some windows of ? (or φ) for maintaining an almost fully spin-polarized Nernst effect exist and their width is under the control of the other phase. Moreover, for the charge Nernst coefficient $N_c$ and spin Nernst coefficient $N_s$ the relationship $N_c(?,\phi )=?N_s(\phi ,?)$ always holds. These results suggest that our proposal may act as a controllable thermospin generator.     

How entangled can a multi-party system possibly be?

The geometric measure of entanglement of a pure quantum state is defined to be its distance to the space of pure product (separable) states. Given an n-partite system composed of subsystems of dimensions $d_1,\dots ,d_n$, an upper bound for maximally allowable entanglement is derived in terms of geometric measure of entanglement. This upper bound is characterized exclusively by the dimensions $d_1,\dots ,d_n$ of composite subsystems. Numerous examples demonstrate that the upper bound appears to be reasonably tight.     

Spin Hall effect and Nernst effect in FePt/Au multi-terminal devices with different Au thicknesses

The spin-Hall effect and the Nernst effect were investigated in multi-terminal devices consisting of an FePt perpendicular spin polarizer and a Au Hall cross with different Au thicknesses. As the thickness of the Au Hall cross increased from 10 nm to 20 nm, the spin-Hall angle (${\alpha }_H$) was significantly reduced. The significant reduction of the spin-Hall angle indicates that the interface and/or surface scattering of the electron spins play a crucial role for the large ${\alpha }_H$. The voltage change due to the Nernst effect also decreased with increasing the thickness of the Au Hall cross.     

Persistent spin current in mesoscopic antiferromagnet spin chain with Dzyaloshinskii–Moriya interaction

By using the modified spin-wave and gauge invariant methods, we show that at zero temperature in the presence of an inhomogeneous magnetic field with magnitude B gives rise to a persistent magnetization current around a mesoscopic antiferromagnetic Heisenberg spin ring with the DM (Dzyaloshinskii–Moriya) interaction. The results show that the persistent magnetization current is vanishing at large $D_s/J$ ($D_s$ is reduced DM interaction and J is nearest exchange coupling) with $\alpha >1$ (α is a constant describing the energy gap of the spin system). The result also shows that under the homogeneous magnetic field there exists a non-zero spin current in the spin ring.     

Percolation on infinitely ramified fractal networks

We study how fractal features of an infinitely ramified network affect its percolation properties. The fractal attributes are characterized by the Hausdorff ($D_H$), topological Hausdorff ($D_{tH}$), and spectral ($d_s$) dimensions. Monte Carlo simulations of site percolation were performed on pre-fractal standard Sierpiński carpets with different fractal attributes. Our findings suggest that within the universality class of random percolation the values of critical percolation exponents are determined by the set of dimension numbers ($D_H$, $D_{tH}$, $d_s$), rather than solely by the spatial dimension (d). We also argue that the relevant dimension number for the percolation threshold is the topological Hausdorff dimension $D_{tH}$, whereas the hyperscaling relations between critical exponents are governed by the Hausdorff dimension $D_H$. The effect of the network connectivity on the site percolation threshold is revealed.     

Investigations of half-metallic ferromagnetism and thermoelectric properties of cubic XCrO3 (X = Ca,Sr,Ba) compounds via first-principles approaches

In this paper, the physical aspects of the cubic phase XCrO₃ ($\mathrm{X}=\mathrm{Ca},\mathrm{Sr},\mathrm{Ba}$) perovskites are studied by employing full-potential linearized augmented plane wave plus local orbital ($\text{FP-LAPW}+\mathit{lo}$) method. These compounds have been found stable in ferromagnetic (FM) phase since they possess lower energy in FM phase compared to non-FM phase and their stability is also confirmed by calculating the enthalpy of formation (ΔH). The electronic structures of these compounds are analyzed with Trans and Blaha modified Becke–Johnson potential (TB-mBJ) for both spin up and spin down channels, which indicate their half-metallic characters. Analysis of density of states (DOS) shows major contributions of O-2p states in the valence band and Cr 3d-state in conduction band. A comparative analysis of crystal field effect ($\mathrm{\Delta }{\mathrm{E}}_{\mathrm{crystal}}$) and the exchange energies (direct ${\mathrm{\Delta }}_x(d)$ and indirect ${\mathrm{\Delta }}_x(pd)$) tells about the main part of electronic spin in ferromagnetic character. The calculated magnetic moments make these compounds favorable for spintronic applications. In the end, thermoelectric parameters are computed for 200 K–800 K temperature range to explore potential of these compounds for applications in renewable energy devices.     

On spacelike hypersurfaces of constant sectional curvature lorentz manifolds

Let $x:M^n\to {\overline{M}}^{n+1}$ be an n-dimensional spacelike hypersurface of a constant sectional curvature Lorentz manifold $\overline{M}$. Based on previous work of S. Montiel, L. Alías, A. Brasil and G. Colares studied what can be said about the geometry of M when $\overline{M}$ is a conformally stationary spacetime, with timelike conformal vector field K. For example, if $M^n$ has constant higher order mean curvatures $H_r$ and $H_{r+1}$, they concluded that $M^n$ is totally umbilical, provided $H_{r+1}\ne 0$ on it. If div($K$) does not vanish on $M^n$ they also proved that $M^n$ is totally umbilical, provided it has, a priori, just one constant higher order mean curvature.In this paper, we compute $L_r(S_r)$ for such an immersion, and use the resulting formula to study both r-maximal spacelike hypersurfaces of $\overline{M}$, as well as, in the presence of a constant higher order mean curvature, constraints on the sectional curvature of M that also suffice to guarantee the umbilicity of M. Here, by $L_r$ we mean the linearization of the second order differential operator associated to the r-th elementary symmetric function $S_r$ on the eigenvalues of the second fundamental form of x.     

Spin-gapped phases in the frustrated Hubbard chain with transverse spin anisotropy

At weak coupling, we investigate the frustrated Hubbard chain including nearest-neighbor and next-nearest-neighbor antiferromagnetic exchange with easy-plane anisotropy $J_1^{xy}$ and $J_2^{xy}$. At half filling, we obtain three different phases in the $J_1^{xy}$–${J_2}^{xy}$ plane: a transverse spin density wave phase, a bond order wave phase and a Luther–Emery metallic phase characterized by the coexistence of singlet superconductivity and charge density wave correlations. The frustrating exchange $J_2^{xy}$ accounts for the spin-gapped phases.     

A physical pathway to understand individual's labeling behavior in signed social networks

In this paper we propose a reshuffling approach to empirical analyze individual's labeling behavior in signed social networks. In our approach, each individual is assumed to have the ability to re-label his/her neighbors randomly with the parameters $p_s$ and $p_{+}$. Many reshuffled networks, which have the same topological structure and different signs' configuration, are built through applying our approach to the given three signed social networks. The entropy $S_{out}$ and the giant component ${\rho }_G$ for each reshuffled networks are calculated and analyzed. We find that there exist two kinds of individual's labeling behavior according to the suppressed effect of $S_{out}$ and the exponent α in the relationship of ${\rho }_G$ and $q_{+}$. Additionally, the suppressed effect of $S_{out}$ shows the non-randomness factor in individual's labeling behavior. These results offer new insights to understand human's behavior in online social networks.     

Finite size effects on calorimetric cooperativity of two-state proteins

Finite size effects on the calorimetric cooperatity of the folding-unfolding transition in two-state proteins are considered using the Go lattice models with and without side chains. We show that for models without side chains a dimensionless measure of calorimetric cooperativity ${\kappa }_2$ defined as the ratio of the van’t Hoff to calorimetric enthalpy does not depend on the number of amino acids N. The average value $\overline{{\kappa }_2}\approx \frac{3}{4}$ is lower than the experimental value ${\kappa }_2\approx 1$. For models with side chains ${\kappa }_2$ approaches unity as ${\kappa }_2\sim N^{\mu }$, where $\mu \approx 0.17$. Above the critical chain length $N_c\approx 135$ these models can mimic the truly all-or-non folding–unfolding transition.     

Impact of local coupling on the vulnerability of 2D spatially embedded interdependent networks

Real networks are always interdependent and spatially embedded. Considering the space constraint, dependency links between networks may be established not globally but locally. In this paper, we study how the spatial coupling will impact the robustness of interdependent scale-free networks located in a 2D square plane where dependent nodes are connected within a connecting radius $r_{connect}$. Besides the traditional assortative degree–degree coupling (GD) and random coupling (GR), some novel spatial couplings are also introduced, i.e., spatial assortative degree–degree coupling (SD), spatial random coupling (SR) and nearest neighbor coupling (NN). Simulation results indicate that assortative couplings, GD and SD, can improve the robustness under topological attacks while under localized attacks, NN coupling is the best one. In addition, for SD coupling under topological attacks, we find that the robustness for small $r_{connect}$ decreases with $r_{connect}$ from 0 to the critical value $r_{c1}$, and for larger $r_{connect}$ gradually increases with $r_{connect}$ from $r_{c1}$ to the maximum value ${(r_{connect})}_{max}$. However, opposite results will be obtained under localized attacks. These findings may be helpful to understand and analyze some real interdependent infrastructures.     

Exact PsTd invariant and PsTd symmetric breaking solutions,symmetry reductions and Bäcklund transformations for an AB–KdV system

In natural and social science, many events happened at different space–times may be closely correlated. Two events, A (Alice) and B (Bob) are defined as correlated if one event is determined by another, say, $B=\stackrel{?}{f}A$ for suitable $\stackrel{?}{f}$ operators. A nonlocal AB–KdV system with shifted-parity ($P_s$, parity with a shift), delayed time reversal ($T_d$, time reversal with a delay) symmetry where $B=\stackrel{?}{P_s}\stackrel{?}{T_d}A$ is constructed directly from the normal KdV equation to describe two-area physical event. The exact solutions of the AB–KdV system, including $P_s{T}_d$ invariant and $P_s{T}_d$ symmetric breaking solutions are shown by different methods. The $P_s{T}_d$ invariant solution show that the event happened at A will happen also at B. These solutions, such as single soliton solutions, infinitely many singular soliton solutions, soliton–cnoidal wave interaction solutions, and symmetry reduction solutions etc., show the AB–KdV system possesses rich structures. Also, a special Bäcklund transformation related to residual symmetry is presented via the localization of the residual symmetry to find interaction solutions between the solitons and other types of the AB–KdV system.     

Dynamical quantum Fisher information in the Ising model

In terms of quantum Fisher information, we discuss the dynamics of quantity ${\chi }^2$ of the Ising model. The inequality ${\chi }^2<1$ detects the class of entangled states which are useful for sub-shot-noise sensitivity. All the exact dynamics of the expectations of collective spin operators are derived. The minimum ${\chi }^2$ in the plane perpendicular to the mean spin direction is analytically given. We find that ${\chi }^2$ does not depend on the system size $N$ when $N\ge 4$. Except for the periodic points, the evolution states are always entangled and useful for the sub-shot-noise phase estimation.