Distribution of electrons and holes in cuprate superconductors as determined from ${}^{17}$O and ${}^{63}$Cu nuclear magnetic resonance

Abstract

The distribution of electrons and holes in the CuO${}_2$ plane of the high-temperature superconducting cuprates is determined with nuclear magnetic resonance through the quadrupole splittings of ${}^{17}$O and ${}^{63}$Cu. Based on new data for single crystals of electron-doped Pr${}_{2-x}$Ce${}_x$CuO${}_4$(x=0, 0.05, 0.10, 0.15) as well as Nd${}_{2-x}$Ce${}_x$CuO${}_4$ (x=0, 0.13) the changes in hole contents $n_d$ of Cu 3d$(x^2-y^2)$ and $n_p$ of O 2$p_{\sigma }$ orbitals are determined and they account for the stoichiometrically doped charges, similar to hole-doped \lsco. It emerges that while $n_d+2n_p=1$ in all parent materials as expected, $n_d$ and $n_p$ vary substantially between different groups of materials. Doping holes increases predominantly $n_p$, but also $n_d$. To the contrary, doping electrons predominantly decreases $n_d$ and only slightly $n_p$. However, $n_p$ for the electron doped systems is higher than that in hole doped La${}_{1.85}$Sr${}_{0.15}$CuO${}_4$. Cuprates with the highest maximum $T_{\mathrm{c}}$s appear to have a comparably low $n_d$ while, at the same time, $n_p$ is very high. The rather high oxygen hole content of the Pr${}_2$CuO${}_4$ and Nd${}_2$CuO${}_4$ with the low $n_d$ seems to make them ideal candidates for hole doping to obtain the highest $T_{\mathrm{c}}$.

5 pages, 5 figures

References in corpus (1)

• Advances in single crystal growth and annealing treatment of electron-doped HTSC

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