Anomalous high energy dispersion in photoemission spectra from insulating cuprates

TL;DR

This study reveals an unexpected high energy dispersion in photoemission spectra of insulating cuprates, showing a close match to unrenormalized band predictions and indicating complex spectral weight transfer and structure in the spectral function.

Contribution

It uncovers a high energy dispersive feature in insulating cuprates that aligns with unrenormalized band theory, highlighting complex spectral structures not previously observed.

Findings

Discovery of a high energy dispersive feature near the unrenormalized band

Observation of spectral weight transfer from low to high energy features

Evidence of complex momentum space structure in the spectral function

Abstract

Angle resolved photoelectron spectroscopic measurements have been performed on an insulating cuprate Ca_2CuO_2Cl_2. High resolution data taken along the \Gamma to (pi,pi) cut show an additional dispersive feature that merges with the known dispersion of the lowest binding energy feature, which follows the usual strongly renormalized dispersion of ~0.35 eV. This higher energy part reveals a dispersion that is very close to the unrenormalized band predicted by band theory. A transfer of spectral weight from the low energy feature to the high energy feature is observed as the \Gamma point is approached. By comparing with theoretical calculations the high energy feature observed here demonstrates that the incoherent portion of the spectral function has significant structure in momentum space due to the presence of various energy scales.