One-dimensional systems with short-range interactions cannot exhibit a long-range order at nonzero temperature. However, there are some particular one-dimensional models, such as the Ising-Heisenberg spin models with a variety of lattice geometries, which exhibit unexpected behavior similar to the discontinuous or continuous temperature-driven phase transition. Although these pseudo-transitions are not true temperature-driven transitions showing only abrupt changes or sharp peaks in thermodynamic quantities, they may be confused while interpreting experimental data. Here we consider the spin-1 2 Ising-XYZ diamond chain in the regime when the model exhibits temperature-driven pseudo-transitions. We provide a detailed investigation of several correlation functions between distant spins that illustrates the properties of quasi-phases separated by pseudo-transitions. Inevitably, all correlation functions show the evidence of pseudo-transition, which are supported by the analytical solutions and, besides we provide a rigorous analytical investigation around the pseudo-critical temperature. It is worth to mention that the correlation functions between distant spins have an extremely large correlation length at pseudo-critical temperature.σ i+r−1 Figure 1: Schematic representation of spin-1 2 Ising-XYZ diamond chain.

Recently has been observed for some one-dimensional models that exhibit unexpected pseudotransitions and quasi-phases. This pseudo-transition resembles a first-and second-order phase transition simultaneously. One of those models is the spin-1/2 Ising-XYZ diamond chain, composed of Ising spin particles at the nodal sites and the Heisenberg spin particles at the interstitial sites. Where we assume Ising-type interaction between the nodal and interstitial sites, the Heisenberg-type interaction between interstitial sites, and with an external magnetic field applied along the z-axis. This model presents an exact analytical solution applying the transfer matrix technique, which shows 3 phases at zero temperature in the vicinity of pseudo-transition. The pseudo-transition separates quasi-phases, these quasi-phases still hold at a finite temperature most of the pattern configurations of a true phase at zero temperature. Here we study the quantum entanglement of pair spin particles in the quasi-phase regions, which can be measured through the concurrence. Then we observe an unexpected behavior in the concurrence, that is below pseudocritical temperature the concurrence remains almost constant up to pseudo-critical temperature, but above the pseudo-critical temperature, the concurrence behaves as for the standard one-dimensional spin models.Further, we consider the entropy behavior of the system, below pseudo-critical temperature the entropy becomes almost null, while above pseudo-critical temperature the system exhibits standard behavior as for ordinary one-dimensional spin models.

We study the local thermal entanglement in a spin-1/2 Ising-XXZ diamond structure with two impurities. In this spin chain, we have the two impurities with an isolated XXZ dimer between them. We focus on the study of the thermal entanglement in this dimer. The main goal of this paper is to provide a good understanding of the effect of impurities in the entanglement of the model. This model is exactly solved by a rigorous treatment based on the transfer-matrix method. Our results show that the entanglement can be tuned by varying the impurities parameters in this system. In addition, it is shown that the thermal entanglement for such a model exhibits a clear performance improvement when we control and manipulate the impurities compared to the original model without impurities. Finally, the impurities can be manipulated to locally control the thermal entanglement, unlike the original model where it is done globally. arXiv:1901.07690v1 [quant-ph] 23 Jan 2019

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