Optical properties of an effective one-band Hubbard model for the cuprates

TL;DR

This paper investigates the optical properties and spectral density of a one-band Hubbard model for cuprates, revealing how doping affects electronic states and optical conductivity, with results aligning qualitatively with experiments at low to moderate doping.

Contribution

It derives and analyzes an effective one-band Hubbard model from a three-band model, providing insights into spectral weight transfer and optical features in doped cuprates.

Findings

Spectral weight transfer depends on original model parameters.

Optical conductivity shows a mid-infrared peak and pseudogap.

Results agree qualitatively with experiments at low to moderate doping.

Abstract

We study the Cu and O spectral density of states and the optical conductivity of CuO_2 planes using an effective generalized one-band Hubbard model derived from the extended three-band Hubbard model. We solve exactly a square cluster of 10 unit cells and average the results over all possible boundary conditions, what leads to smooth functions of frequency. Upon doping, the Fermi energy jumps to Zhang-Rice states which are connected to the rest of the valence band (in contrast to an isolated new band in the middle of the gap). The transfer of spectral weight depends on the parameters of the original three-band model not only through the one-band effective parameters but also through the relevant matrix elements. We discuss the evolution of the gap upon doping. The optical conductivity of the doped system shows a mid-infrared peak due to intraband transitions, a pseudogap and a high frequency part related to interband transitions. Its shape and integrated weight up to a given frequency (including the Drude weight) agree qualitatively with experiments in the cuprates for low to moderate doping levels, but significant deviations exist for doping $x>0.3$.