Possible observation of string excitations of a hole in a quantum antiferromagnet

We argue that recently reported high resolution angle-resolved photoelectron spectra from cuprates, where an anomalous high-energy dispersion was identified, reveal the internal structure of the hole quasiparticle in quantum antiferromagnets and more importantly it is evidence for the existence of string-excitations which validate early predictions based on the t-J model. Their energy-momentum dispersion, the manner in which the spectral weight is transfered to higher energy string excitations, and the vanishing of the quasiparticle spectral weight near the F point, are all in agreement with predictions without adjusting any parameters. (c) 2006 Elsevier B.V. All rights reserved.