Measurement of x-ray absorption spectra of overdoped high-temperature cuprate superconductors: Inapplicability of the single-band Hubbard model

TL;DR

This study uses x-ray absorption spectra to show that the electronic structure of overdoped cuprate superconductors significantly deviates from predictions of the single-band Hubbard model, indicating a need for new theoretical approaches.

Contribution

It demonstrates the inapplicability of the single-band Hubbard model in the overdoped regime of high-temperature cuprate superconductors based on spectroscopic evidence.

Findings

Absence of the upper Hubbard band in overdoped samples

Reduced intensity of the prepeak above p ~ 0.21

Breakdown of the Zhang-Rice singlet approximation

Abstract

X-ray absorption spectra on the overdoped high-temperature superconductors Tl_2Ba_2CuO_{6+delta} (Tl-2201) and La_{2-x}Sr_xCuO_{4+delta} (LSCO) reveal a striking departure in the electronic structure from that of the underdoped regime. The upper Hubbard band, identified with strong correlation effects, is not observed on the oxygen K edge, while the lowest-energy prepeak gains less intensity than expected above p ~ 0.21. This suggests a breakdown of the Zhang-Rice singlet approximation and a loss of correlation effects or a significant shift in the most fundamental parameters of the system, rendering single-band Hubbard models inapplicable. Such fundamental changes suggest that the overdoped regime may offer a distinct route to understanding in the cuprates.