Pairwise entanglement and critical behavior of an anisotropic ferrimagnetic spin chain

There are several measures of entanglement for two qubits, so it is natural to study criticality with quantum-information concepts in the context of Heisenberg spin-1/2 chains, say, by taking a pair of spins at the center. It turns out that this can be generalized to mixed-spin chains with $(S,s)=(S,1/2)$

The simplest case is to consider a system with $(S,s)=(1,1/2)$. By adding uniaxial crystal-field anisotropy $D$ on the spin-1, a realization of the system is found in the compound NiCu(pba)(D$_2$O)$_3$2D$_2$O. This system has a quantum magnetization plateaux at 1/3 of its saturation magnetization.

Investigating the critical behavior in such systems using quantum-information tools was an unexplored terrain. So, by incorporating entanglement measures into DMRG, I was able to estimate the value of $D$ for which the plateaux disappears and the order of the corresponding quantum phase transition.