Charge dynamics in an ideal cuprate $Ca_{2-x} Na_x Cu O_2 Cl_2$: optical conductivity from Yang-Rice-Zhang ansatz

TL;DR

This paper uses the Yang-Rice-Zhang ansatz to theoretically analyze charge dynamics in underdoped cuprate CNCOC, revealing limitations of the ansatz and emphasizing the need for additional physics to fully explain experimental optical conductivity data.

Contribution

It applies the YRZ ansatz to model optical conductivity in CNCOC and critically assesses its adequacy, highlighting the necessity of including bound charge effects.

Findings

YRZ ansatz reproduces some experimental features

Extended Drude analysis shows limitations of the ansatz

Additional physics needed for complete understanding

Abstract

We theoretically investigate charge dynamics in weakly coupled $CuO_2$ planes of the cuprate $Ca_{2-x} Na_x Cu O_2 Cl_2$ (CNCOC) using Kubo formula for optical conductivity in the underdoped regime. The spectral function needed in Kubo formula is obtained from an analytical form of electron Green's function proposed (ansatz) by Yang-Rice-Zhang (YRZ) for the underdoped cuprates based on their previous renormalized mean field theory and on the investigations of weakly coupled Hubbard ladders. Although to an unaided eye the results of the numerical calculation look very similar to that found experimentally in [K. Waku etal. 2004] but a careful examination with extended Drude formalism shows that YRZ ansatz for the calculation of optical conductivity is not sufficient to understand the charge dynamics in $CuO_2$ planes of the cuprate CNCOC. More physics is needed especially electromagnetic response from bound charges.