Unconventional Thermal and Magnetic-Field-Driven Changes of a Bipartite Entanglement of a Mixed Spin-(1/2,S) Heisenberg Dimer with an Uniaxial Single-Ion Anisotropy.

Hana Vargová,Jozef Strečka

doi:10.3390/nano11113096

Abstract

The concept of negativity is adapted in order to explore the quantum and thermal entanglement of the mixed spin-(1/2,S) Heisenberg dimers in presence of an external magnetic field. The mutual interplay between the spin size S, XXZ exchange and uniaxial single-ion anisotropy is thoroughly examined with a goal to tune the degree and thermal stability of the pairwise entanglement. It turns out that the antiferromagnetic spin-(1/2,S) Heisenberg dimers exhibit higher degree of entanglement and higher threshold temperature in comparison with their ferromagnetic counterparts when assuming the same set of model parameters. The increasing spin magnitude S accompanied with an easy-plane uniaxial single-ion anisotropy can enhance not only the thermal stability but simultaneously the degree of entanglement. It is additionally shown that the further enhancement of a bipartite entanglement can be achieved in the mixed spin-(1/2,S) Heisenberg dimers, involving half-odd-integer spins S. Under this condition the thermal negativity saturates at low-enough temperatures in its maximal value regardless of the magnitude of half-odd-integer spin S. The magnetic field induces consecutive discontinuous phase transitions in the mixed spin-(1/2,S) Heisenberg dimers with , which are manifested in a surprising oscillating magnetic-field dependence of the negativity observed at low enough temperature.

Highlights

Extraordinary correlations between subsystems of a quantum-mechanical ensemble, known as entanglement, belongs to the most fascinating phenomena attracting a lot of attention during the last few decades
In order to minimize the reduction of the degree of entanglement, many of subsequent studies were concentrated on an extended mixedspin Heisenberg chain involving the Dzyaloshinskii–Moriya interaction (DMI) [34,35,36,37], the effect of nonuniform magnetic field [37,38,39,40,41,42,43], long-range interaction [44] and uniaxial single-ion anisotropy [45,46], respectively
It was verified for the mixed spin-(1/2,1), spin-(1/2,3/2) and spin-(1/2,5/2) Heisenberg chains that the inhomogeneity of the external magnetic field can be suitable tuning parameter for enhancing the thermal entanglement in a high-temperature region

Summary

Introduction

Extraordinary correlations between subsystems of a quantum-mechanical ensemble, known as entanglement, belongs to the most fascinating phenomena attracting a lot of attention during the last few decades. In order to minimize the reduction of the degree of entanglement, many of subsequent studies were concentrated on an extended mixedspin Heisenberg chain involving the Dzyaloshinskii–Moriya interaction (DMI) [34,35,36,37], the effect of nonuniform magnetic field [37,38,39,40,41,42,43], long-range interaction [44] and uniaxial single-ion anisotropy [45,46], respectively It was verified for the mixed spin-(1/2,1), spin-(1/2,3/2) and spin-(1/2,5/2) Heisenberg chains that the inhomogeneity of the external magnetic field can be suitable tuning parameter for enhancing the thermal entanglement in a high-temperature region.

Model and Method

Results and Discussion

Quantum Negativity

The Thermal Negativity

Conclusions