Effect of an uniaxial single-ion anisotropy on the quantum and thermal entanglement of a mixed spin-(1/2, [formula omitted]) Heisenberg dimer

Abstract

Exact analytical diagonalization is used to study the bipartite entanglement of the antiferromagnetic mixed spin-(1/2, S) Heisenberg dimer (MSHD) with the help of negativity. Under the assumption of uniaxial single-ion anisotropy affecting higher spin-S (S>1/2) entities only, the ground-state degeneracy 2S is partially lifted and the ground state is two-fold degenerate with the total magnetization per dimer ±(S−1/2). It is shown that the largest quantum entanglement is reached for the antiferromagnetic ground state of MSHD with arbitrary half-odd-integer spins S regardless of the exchange and single-ion anisotropies. Contrary to this, the degree of a quantum entanglement in MSHD with an integer spin S exhibits an increasing tendency with an obvious spin-S driven crossing point, when assuming the easy-plane single-ion anisotropy. It is shown that the increasing spin magnitude is a crucial driving mechanism for an enhancement of a threshold temperature above which the thermal entanglement vanishes. The easy-plane single-ion anisotropy together with an enlargement of the spin-S magnitude is other significant driving mechanism for an enhancement of the thermal entanglement in MSHD.