We investigate how the transition from integrability to nonintegrability occurs by changing the parameters of the Hamiltonian of a Heisenberg spin-1/2 chain with defects. Randomly distributed defects may lead to quantum chaos. A similar behavior is obtained in the presence of a single defect out of the edges of the chain, suggesting that randomness is not the cause of chaos in these systems, but the mere presence of a defect.
@article{arxiv.cond-mat/0310035,
title = {Integrability of a disordered Heisenberg spin-1/2 chain},
author = {L. F. santos},
journal= {arXiv preprint arXiv:cond-mat/0310035},
year = {2009}
}