Entanglement and quantum phase transition in a mixed-spin Heisenberg chain with single-ion anisotropy

In the mixed-spin $(S,s)=(1,1/2)$ Heisenberg chain with crystal-field anisotropy $D$ on the $S=1$ ions, the ground state is doubly degenerate (with ferrimagnetic long-range order) for $D<0$, and it is unique for $D>0$. So the $D=0$ is a bifurcation point. I was interested in what happens to pairwise entanglement measures during the corresponding quantum phase transition, specially as the temperature is varied.

As expected, the entanglement vanishes at a threshold temperature that increases by increasing $|D|$. Remarkably, it is more robust against temperature changes in the easy-plane regime ($D>0$) than in the easy axis regime ($D<0$), in the sense that the quantum behavior survives at higher temperatures. This is interesting because the crystal-field anisotropy can be increased locally in experiments by adding non-magnetic defects.