Entanglement of periodic anisotropic XY chains

By using the concept of concurrence, the entanglement of periodic anisotropic XY chains in a transverse field is studied numerically. It is found that the derivatives partial derivative lambda C(1) of nearest-neighbour concurrence diverge at quantum critical points. By proper scaling, we found that all the derivatives partial derivative lambda C (1) for periodic XY chains in the vicinity of quantum critical points have the same behaviours as that of a uniform chain.