title: Dynamically dominant excitations of string solutions in the spin-1/2 antiferromagnetic Heisenberg chain in a magnetic field.
abstract: Using Bethe-ansatz solutions, this Letter uncovers a well-defined continuum in dynamical structure factor S+-(k,omega) of the spin-1/2 antiferromagnetic Heisenberg chain in magnetic fields. It comes from string solutions that continuously connect the mode of the lowest-energy excitations in the zero-field limit and that of bound states of overturned spins from the ferromagnetic state near the saturation field. The relevance to real materials is confirmed through comparisons with experimental results.
authors.affiliation: WPI Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba 305-0047, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Kohno