Determination of doped charge density in superconducting cuprates from NMR or stripes

TL;DR

This paper uses NQR and stripe models to accurately determine doped charge densities in high-$T_c$ cuprates, confirming the localization of doped holes and electrons at specific atomic sites and providing insights into their electronic structure.

Contribution

It validates the stripe model's assumptions about hole and electron localization in cuprates using NQR data, and refines the understanding of doped charge distribution in various high-$T_c$ materials.

Findings

Doped-hole density $h$ closely matches itinerant hole density $ ilde{p}$ from stripe incommensurability.

NQR confirms hole residence at oxygen sites and electrons at copper sites in specific cuprates.

Doped-hole probabilities in oxygen and copper orbitals are approximately 1/2 and 2/3, respectively, in oxygen-enriched cuprates.

Abstract

Independent investigations of nuclear quadrupole resonance (NQR) and of stripes in high-$T_c$ cuprates find a small deviation of doped-hole density $h$ from the doping level of $La_{2-x}Sr_xCuO_4$. The value observed with NQR, $ x - h \approx 0.02$, agrees closely with the density of itinerant holes, $\tilde{p}$, responsible for suppression of 3D-AFM, as obtained from stripe incommensurability. The stripe model's assumption that doped holes in $La_{2-x}Sr_xCuO_4$ reside at oxygen sites, and that doped electrons in $Ln_{2-x}Ce_xCuO_4$ ($Ln = Pr, Nd$) reside at copper sites, is (to a large degree) confirmed with NQR. The NQR finding of doped-hole probabilities in oxygen and copper orbitals of $HgBa_2CuO_{4+\delta}$ and other oxygen-enriched high-$T_c$ cuprates, $P_p \simeq P_d \simeq 1/2$, as well as of oxygen-doped $YBa_2Cu_3O_{6+y}$, $P_p \simeq 2P_d \simeq 2/3$, is interpreted with the stripe model in terms of excess oxygen atoms in the $CuO_2$ planes and $CuO$ chains.