Bipartite entanglement in Heisenberg spin ladder with ferro- and antiferromagnetic couplings.

In this paper, the spin ladder consisting of two antiferromagnetic Heisenberg legs is investigated by means of the density matrix renormalization group method with its matrix product state form. The energy density and bipartite entanglement measured by concurrence are calculated, the effects of interleg couplings and open boundary condition on entanglement distributions are discussed in detail when the interleg couplings are ferro- and antiferromagnetic, respectively. We found that the entanglements are mainly distributed in legs and diagonals when the interleg couplings are ferromagnetic and in rungs when the couplings are antiferromagnetic. Furthermore, the intraleg entanglements are more affected by the dimerization caused by open boundary than interleg ones. Specifically, that dimerization will be weakened by the interleg couplings, and the entanglements are distributed more uniformly. [ABSTRACT FROM AUTHOR]