Charge excitations in a quantum antiferromagnet

We briefly report momentum-resolved charge excitations in a cuprate antiferromagnetic insulator in the intermediate regimes of momentum transfers using high energy resonant X-ray scattering near the Cu K-edge. The excitation spectra show dispersive features near the insulating gap edge which can be understood in terms of antiferromagnetic correlation of the underlying lattice. Details of the experiment will be reported elsewhere. (C) 2001 Published by Elsevier Science B.V.