Non-classical correlations in a Heisenberg spin model with Heitler–London approach

The isotropic Heisenberg two-spin-1/2 model in the XXX configuration under an external transverse nonuniform magnetic field is considered at thermal equilibrium. In the context of the Heitler–London approach, the variation of the spin–spin exchange coupling strength in terms of the position is adopted. The effects of the inter-spin relative coupling distance r and nonuniform magnetic field on the thermal evolution of quantum correlations are studied in detail. By tuning the coupling distance r, temperature T and nonuniform magnetic field B, quantum correlations can be scaled in the bipartite system. Astonishingly, we find the long sustainable behavior of geometric quantum discord in comparison with entanglement over the coupling distance r. Moreover, we show the existence of separable quantum states with nonzero quantum correlations in terms of trace discord. Besides, the quantum correlations shared between the considered bipartite system parts are only the entanglement type for a fixed temperature and suitable strong nonuniform magnetic field values. An entangled-unentangled phase transition at \(T=0.1\) with threshold relative distance \(r_f\) can be detected by the entanglement behavior in terms of B and r. A kind of correspondence between thermal entanglement and thermal non-classical correlations for a strong value of B can be observed. It is our hope that this research may open a new path to consider the role of Heitler–London approach in non-classical correlations preservation.