title: Fractional and integer excitations in quantum antiferromagnetic spin 1/2 ladders.
abstract: Spectral densities are computed in unprecedented detail for quantum antiferromagnetic spin 1/2 two-leg ladders. These results were obtained due to a major methodical advance achieved by optimally chosen unitary transformations. The approach is based on dressed integer excitations. Considerable weight is found at high energies in the two-particle sector. Precursors of fractional spinon physics occur supporting the conclusion that there is no necessity to resort to fractional excitations in order to describe features at higher energies.
authors.affiliation: Institut für Theoretische Physik, Universität zu Köln, Zülpicher Strasse 77, D-50937 Köln, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Knetter
authors.forename: K P
authors.initials: KP
authors.lastname: Schmidt
authors.forename: M
authors.initials: M
authors.lastname: Grüninger
authors.forename: G S
authors.initials: GS
authors.lastname: Uhrig