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

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 MSH D with arbitrar y half-odd-integer spins S regardless of the exchange and single-ion anisotropies. Contra r y to this, the degree of a quantum entanglement in MSH D 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.

Automated summary

Exact analytical diagonalization is used to study the bipartite entanglement of the antiferromagnetic mixed spin-(1/2, S) Heisenberg dimer. The largest quantum entanglement is found in the antiferromagnetic ground state of MSHD for arbitrary half-odd-integer spins S, regardless of exchange and single-ion anisotropies. In contrast, the degree of quantum entanglement in MSHD with an integer spin S exhibits an increasing tendency with an obvious spin-S driven crossing point when assuming easy-plane single-ion anisotropy. Increasing spin magnitude and easy-plane single-ion anisotropy are significant driving mechanisms for enhancing thermal entanglement in MSHD.