Energy versus magnetic field diagram of the spin-1 Haldane system with an impurity

Abstract

Energy versus magnetic field diagram of the spin-1 Haldane system with an impurity bond is studied in terms of spin- 1 2 degrees of freedom at the sites neighboring the impurity bond by means of an analytical method. We examine the equivalence between a phenomenological Hamiltonian of two coupled spin- 1 2 spins representing the spin- 1 2 degrees of freedom and a more realistic Hamiltonian. It is shown that when the strength of the impurity bond is sufficiently weak, the two Hamiltonians are equivalent to each other, as far as the energies of low-lying states are concerned.