title: Novel longitudinal mode in the coupled quantum chain compound KCuF3
abstract: Inelastic neutron scattering measurements are reported that show a new longitudinal mode in the antiferromagnetically ordered phase of the spin- 1/2 quasi-one-dimensional antiferromagnet KCuF3. This mode signals the crossover from one-dimensional to three-dimensional behavior and indicates a reduction in the ordered spin moment of a spin- 1/2 antiferromagnet. The measurements are compared with recent quantum field theory calculations and are found to be in excellent agreement. A feature of the data not predicted by theory is a damping of the mode by decay processes to the transverse spin-wave branches.
authors.affiliation: Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, USA.
authors.initials: B
authors.lastname: Lake
authors.initials: DA
authors.lastname: Tennant
authors.initials: SE
authors.lastname: Nagler