Eur. Phys. J. B 83, 329-335 (2011)
https://doi.org/10.1140/epjb/e2011-20412-7

Regular Article

Concurrence and entanglement entropy in a dimerised spin-1/2 two-leg ladder

Department of Physics, University of Guilan, 41335-1914 Rasht, Iran

^a e-mail: mahdavifar@guilan.ac.ir

Received: 1 June 2011
Received in final form: 14 August 2011
Published online: 12 October 2011

Abstract

We consider isotropic spin-1/2 two-leg ladders with dominant spatially-modulated rung exchanges. We study the effect of a uniform magnetic field on the ground state phase diagram of the model using perturbation theory and the numerical Lanczos method. The ground state phase diagram consists of two gapless Luttinger liquid (LL) and three gapped phases. Numerically, we calculate the concurrence between two spins and the entanglement entropy between legs. Numerical experiment shows that the gapless LL phases are fundamentally different. In the first LL phase, only spins on rungs are entangled, but in the second LL phase the spins on legs are long-distance entangled. Therefore, the concurrence between spins on legs can be considered as a function to distinguish the LL phases.