Entanglement in the 1D extended anisotropic Heisenberg model

We present a study of entanglement in the case of the I D extended anisotropic Heisenberg model. We investigate two quantum phase transitions (QPTs) within the previously found ergodicity phase diagram [E. Plekhanov, A. Avella, F. Mancini, Phys. Rev. B 74 (2006) 115120]. Our calculations are done by means of the numerically exact Lanczos method at T = 0, followed by a finite-size scaling. As a measure of entanglement we use the concurrence for two spins out of the system. We conclude from our studies that these QPTs are accompanied by a qualitative entanglement change. (C) 2007 Elsevier B.V. All rights reserved.