Sharp Photoemission Spactra in the Quantum Antiferromagnet

TL;DR

This paper investigates the low-energy photoemission spectra in quantum antiferromagnets, revealing degenerate hole eigenstates and a sharp spectral weight change at the magnetic Brillouin zone surface, aligning with experimental observations.

Contribution

It provides approximation-free calculations and rigorous theorems showing degeneracy and spectral effects in quantum antiferromagnets' photoemission spectra.

Findings

Degeneracy of hole eigenstates with momenta differing by Q.

Presence of a well-defined quasiparticle with zero magnon energy.

Sharp spectral weight change at the magnetic Brillouin zone surface.

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.