PROBLEM OF 2 SPIN DEVIATIONS IN A LINEAR CHAIN WITH NEXT-NEAREST-NEIGHBOR INTERACTIONS

The problem of two spin deviations from the fully aligned state is studied in a linear chain for the Hamiltonian [J(i, j) > 0]: H = -1/2 Σ(nn) J(i, j)Si · Sj - 1/ 2αΣ(nnn)J(i, j)Si · Sj, where (nn) and (nnn) mean nearest- and next-nearest-neighbor interactions, respectively. The behavior of the bound state, which is found to exist for α ≥ 0 only, is discussed.