Momentum and excitation energy dependence of the "waterfalls" in cuprates

TL;DR

This study uses high-resolution photoemission spectroscopy to analyze the 'waterfalls' in cuprates, revealing their dependence on momentum, photon energy, and matrix element effects, challenging previous interpretations of these features as intrinsic.

Contribution

It demonstrates that the high-energy 'waterfall' dispersion in cuprates is primarily due to matrix element effects, not intrinsic spectral features, revising understanding of their electronic structure.

Findings

Waterfalls vary with momentum and photon energy.

Resonant photoemission at Cu 3p3d edge influences observed dispersion.

Waterfalls are caused by matrix element effects, not intrinsic properties.

Abstract

Using high-resolution angle-resolved photoemission spectroscopy we have studied the momentum and photon energy dependence of the anomalous high-energy dispersion, termed "waterfalls", between the Fermi level and 1 eV binding energy in several high-Tc superconductors. We observe strong changes of the dispersion between different Brillouin zones and a strong dependence on the photon energy around 75 eV, which we associate with the resonant photoemission at the Cu 3p3d_{x^2-y^2} edge. We conclude that the high-energy "waterfall" dispersion results from a strong suppression of the photoemission intensity at the center of the Brillouin zone due to matrix element effects and is, therefore, not an intrinsic feature of the spectral function. This indicates that the new high energy scale in the electronic structure of cuprates derived from the "waterfall"-like dispersion may be incorrect.