Magnetization Process in the Shastry-Sutherland System SrCu_<b>2</b>(BO_<b>3</b>)_<b>2</b>: Results of Third-Order Dimer Expansion

Abstract

The magnetization process in the Shastry-Sutherland system is studied by using the third-order perturbation expansion. It is shown that the 1/3-plateau is realized by the second-order perturbation, which is not prevented by the off-diagonal part. In each subspace whose magnetization per dimer is less than 1/3, the lowest energy state is determined by a small but finite energy-gain due to the third-order correlated flip terms and there exists no plateau originating from the third-order effect. Our results are compared with those of the exact diagonalization method to discuss the validity of truncation of states in our perturbation theory.