We examine the thermal entanglement of $XXZ$ -type Heisenberg chains in the presence of a uniform magnetic field along the $z$ axes through the evaluation of the negativity associated with bipartitions of the whole system and subsystems. Limit temperatures for nonzero global negativities are shown to depend on the asymmetry $\ensuremath{\Delta}$, but not on the uniform field, and can be much higher than those limiting pairwise entanglement. It is also shown that global bipartite entanglement may exist for $T>0$ even for $\ensuremath{\Delta}\ensuremath{\geqslant}1$, i.e., when the system is fully aligned (and hence separable) at $T=0$ , and that the bipartition leading to the highest limit temperature depends on $\ensuremath{\Delta}$.We examine the thermal entanglement of $XXZ$-type Heisenberg chains in the presence of a uniform magnetic field along the $z$ axes through the evaluation of the negativity associated with bipartitions of the whole system and subsystems. Limit temperatures for nonzero global negativities are shown to depend on the asymmetry $\ensuremath{\Delta}$, but not on the uniform field, and can be much higher than those limiting pairwise entanglement. It is also shown that global bipartite entanglement may exist for $T>0$ even for $\ensuremath{\Delta}\ensuremath{\geqslant}1$, i.e., when the system is fully aligned (and hence separable) at $T=0$, and that the bipartition leading to the highest limit temperature depends on $\ensuremath{\Delta}$.

arXiv:1112.1279Physical Review AFeb 28, 200638 citations

We examine the thermal entanglement of

XXZ

-type Heisenberg chains in the presence of a uniform magnetic field along the

z

axes through the evaluation of the negativity associated with bipartitions of the whole system and subsystems. Limit temperatures for nonzero global negativities are shown to depend on the asymmetry $\ensuremath{\Delta}$, but not on the uniform field, and can be much higher than those limiting pairwise entanglement. It is also shown that global bipartite entanglement may exist for

T>0

even for $\ensuremath{\Delta}\ensuremath{\geqslant}1$, i.e., when the system is fully aligned (and hence separable) at

T=0

, and that the bipartition leading to the highest limit temperature depends on $\ensuremath{\Delta}$.