Theoretical study of the structural dependence of nuclear quadrupole frequencies in high-Tc superconductors.

Abstract

The remarkable difference between the nuclear quadrupole frequencies ${\ensuremath{\nu}}_{Q}$ of Cu(1) and Cu(2) in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6}$ and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ is analyzed. We calculate the ionic contribution to the electric field gradients and estimate, by using experimental results for ${\mathrm{Cu}}_{2}$O and ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$, the contribution of the d valence electrons. Thus, we determine ${\ensuremath{\nu}}_{Q1}$, ${\ensuremath{\nu}}_{Q2}$, and the asymmetry parameter \ensuremath{\eta} for ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6}$ and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. The number of holes in the Cu-O planes and chains is found to be important for the different behavior of ${\ensuremath{\nu}}_{Q1}$ and ${\ensuremath{\nu}}_{Q2}$.