Effect of Spin-1 Impurities in Dimerized Heisenberg Chains,

P. HANSEN, J. A. RIERA , A. DELIA, E. DAGOTTO

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Lugar: New York; Año: 1998 vol. 58 p. 1 - 10

1098-0121

Lanczos diagonalization and quantum Monte Carlo simulations. First, the magnitude of the interaction betweena Ni ion replacing a Cu ion is derived for the case study system Cu-O-Cu. Then, it is shown that theintroduction of S51 impurities leads to the suppression of the original spin gap of the dimerized system andto the enhancement of the antiferromagnetic correlations close to the impurity. These features are interpreted interms of a valence bond picture of the ground state of both the pure and the doped system. The similitudes anddifferences between the underlying mechanisms that produce these effects in the cases of nonmagnetic andS51 impurities are analyzed. It is stressed that a singlet formed between the spin-1 impurity site and the twospin-1/2 neighbors spins behaves as an effective nonmagnetic vacancy which may be partially responsible forthe enhancement of the antiferromagnetic correlations on the whole system. Implications of these results forexperiment are also discussed.