Updated tests of scaling and universality for the spin-spin correlations in the 2D and 3D spin-S Ising models using high-temperature expansions

We have extended, from order 12 through order 25, the high-temperature series expansions (in zero magnetic field) for the spin-spin correlations of the spin-S Ising models on the square, simple-cubic and body-centered-cubic lattices. On the basis of this large set of data, we confirm accurately the validity of the scaling and universality hypotheses by resuming several tests which involve the correlation function, its moments and the exponential or the second-moment correlation-lengths.Comment: 21 pages, 8 figure

Contribution to Viscosity from the Structural Relaxation via the Atomic Scale Green-Kubo Stress Correlation Function

We studied the connection between the structural relaxation and viscosity for a binary model of repulsive particles in the supercooled liquid regime. The used approach is based on the decomposition of the macroscopic Green-Kubo stress correlation function into the correlation functions between the atomic level stresses. Previously we used the approach to study an iron-like single component system of particles. The role of vibrational motion has been addressed through the demonstration of the relationship between viscosity and the shear waves propagating over large distances. In our previous considerations, however, we did not discuss the role of the structural relaxation. Here we suggest that the contribution to viscosity from the structural relaxation can be taken into account through the consideration of the contribution from the atomic stress auto-correlation term only. This conclusion, however, does not mean that only the auto-correlation term represents the contribution to viscosity from the structural relaxation. Previously the role of the structural relaxation for viscosity has been addressed through the considerations of the transitions between inherent structures and within the mode-coupling theory by other authors. In the present work, we study the structural relaxation through the considerations of the parent liquid and the atomic level stress correlations in it. The comparison with the results obtained on the inherent structures also is made. Our results suggest that in the supercooled liquid regime the vibrational contribution to viscosity extends over the times which are much larger than the Einstein's vibrational period and much larger than the times which it takes for the shear waves to propagate over the model systems. Besides addressing the atomic level shear stress correlations, we also studied correlations between the atomic level pressure elements.Comment: 16 pages, 12 figure

Evidence of a spin liquid phase in the frustrated honeycomb lattice

In the present paper we present some new data supporting the existence of a spin-disordered phase in the Heisenberg model on the honeycomb lattice with antiferromagnetic interactions up to third neighbors along the line J2=J3, predicted in [Phys. Rev. B 83, 094506 (2011)]. We use the Schwinger boson technique followed by a mean field decoupling and exact diagonalization for small systems to show the existence of an intermediate phase with a spin gap and short range N\'eel correlations in the strong quantum limit (S=1/2).Comment: 6 pages, to be published in Modern Physics Letters

Quantum disordered phase on the frustrated honeycomb lattice

In the present paper we study the phase diagram of the Heisenberg model on the honeycomb lattice with antiferromagnetic interactions up to third neighbors along the line $J_2=J_3$ that include the point $J_2=J_3=J_1/2$, corresponding to the highly frustrated point where the classical ground state has macroscopic degeneracy. Using the Linear Spin-Wave, Schwinger boson technique followed by a mean field decoupling and exact diagonalization for small systems we find an intermediate phase with a spin gap and short range N\'eel correlations in the strong quantum limit (S=1/2). All techniques provide consistent results which allow us to predict the existence of a quantum disordered phase, which may have been observed in recent high-field ESR measurements in manganites.Comment: 4 figure

Decision-making model on sustainable supply chain finance under uncertainties

Supply chain finance has received increasing attention. The combination of sustainable development and supply chain finance requires a deeper discussion to address the theoretical and managerial gaps. Thus, this study adopts the fuzzy Technique for Order of Preference by Similarity to Ideal Solution (fuzzy TOPSIS) to develop a sustainable supply chain finance model under uncertainty to identify the existing problems and deficiencies of financing patterns. Expert assessments were performed, and the results indicate that economic factors have a significant effect on other aspects and that delivery management policies are the most effective tools for reinforcing sustainable supply chain finance practices. Moreover, the findings provide a theoretical foundation that can reinforce the understanding of sustainable supply chain finance, and the managerial implications provide a precise guideline for firms to improve their performance.<br/

Density Matrix Embedding from Broken Symmetry Lattice Mean-Fields

Several variants of the recently proposed Density Matrix Embedding Theory (DMET) [G. Knizia and G. K-L. Chan, Phys. Rev. Lett. 109, 186404 (2012)] are formulated and tested. We show that spin symmetry breaking of the lattice mean-field allows precise control of the lattice and fragment filling while providing very good agreement between predicted properties and exact results. We present a rigorous proof that at convergence this method is guaranteed to preserve lattice and fragment filling. Differences arising from fitting the fragment one-particle density matrix alone versus fitting fragment plus bath are scrutinized. We argue that it is important to restrict the density matrix fitting to solely the fragment. Furthermore, in the proposed broken symmetry formalism, it is possible to substantially simplify the embedding procedure without sacrificing its accuracy by resorting to density instead of density matrix fitting. This simplified Density Embedding Theory (DET) greatly improves the convergence properties of the algorithm

Exotic disordered phases in the quantum J1−J2J_1-J_2 model on the honeycomb lattice

We study the ground-state phase diagram of the frustrated quantum $J_1-J_2$ Heisenberg antiferromagnet on the honeycomb lattice using a mean field approach in terms of the Schwinger boson representation of the spin operators. We present results for the ground-state energy, local magnetization, energy gap and spin-spin correlations. The system shows magnetic long range order for $0\leq J_{2}/J_{1}\lesssim 0.2075$ (N\'eel) and $0.398\lesssim J_{2}/J_{1}\leq 0.5$ (spiral). In the intermediate region, we find two magnetically disordered phases: a gapped spin liquid phase which shows short-range N\'eel correlations $(0.2075 \lesssim J_{2}/J_{1} \lesssim 0.3732)$, and a lattice nematic phase $(0.3732 \lesssim J_{2}/J_{1}\lesssim 0.398)$, which is magnetically disordered but breaks lattice rotational symmetry. The errors in the values of the phase boundaries which are implicit in the number of significant figures quoted, correspond purely to the error in the extrapolation of our finite-size results to the thermodynamic limit.Comment: 11 pages, 9 figures, to appear in Phys. Rev.