Sharp Photoemission Spactra in the Quantum Antiferromagnet

Abstract

The low energy photoemission spectra in quantum antiferromagnets are studied by using several approximation-free calculations and rigorous theorems. The important and measurable property found is that the hole eigenstates with momenta differing by the antiferromagnetic wavevector $Q$ are equivalent and degenerate in energy. However the corresponding eigenstates differs by the presence or the absence of a well defined quasiparticle corresponding to a singular -zero energy- magnon, carrying spin one and momentum $Q$. This difference between the two eigenstates affects dramatically the spectral weight as a function of the scattered momentum, since a sharp effect at the surface of the magnetic Brillouin zone is predicted, in apparent agreement with recent experimental data.