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

Abstract

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 despersion as well as the manner in which the spectral weight is transfered to higher energy string excitations as well as the vanishing of the quasiparticle spectral weight near the $\Gamma$ point, are all in agreement with predictions without adjusting any parameters.