title: Low-lying magnetic excitation of the Shastry-Sutherland model.
abstract: By using perturbation calculation and numerical diagonalization, the low-energy spin dynamics of the Shastry-Sutherland model is investigated with particular attention to the two-particle coherent motion. In addition to spin-singlet- and triplet-bound states, we find novel branches of coherent motion of a bound quintet pair, which are usually unstable because of repulsion. Unusual dispersion observed in neutron-scattering measurements is explained by the present theory. The importance of the effects of phonons is also pointed out.
authors.affiliation: Department of Physics, Kyushu University, Fukuoka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Totsuka
authors.forename: S
authors.initials: S
authors.lastname: Miyahara
authors.forename: K
authors.initials: K
authors.lastname: Ueda