Comment on: ``Using Ni Substitution and ${}^{17}$O NMR to Probe the Susceptibility ${\chi }^{\prime }(q)$ in Cuprates''

Abstract

In a recent letter (PRL 79, 2117 (1997)), Bobroff et al. presented novel ${}^{17}$O NMR measurements for YBa_2(Cu_{1-x}Ni_x)_3O_{6+y} which offer a new probe of the momentum dependence of the static spin susceptibility ${\chi }^{\prime }(q)$. They analyzed the ${}^{17}$O line width by assuming a Gaussian form for ${\chi }^{\prime }$, and came to the conclusion that the correlation length $\xi$ is independent of temperature $T$. Furthermore, they claim that a Lorentzian form of ${\chi }^{\prime }$ yields the same result. We will demonstrate that the Lorentzian and Gaussian form of ${\chi }^{\prime }$ actually yield qualitatively different results for the ${}^{17}$O line width and its dependence on $\xi$. We show that their data when combined with $T_{2G}$ data from Takigawa require that $\xi$ be T-dependent. Furthermore, assuming a Gaussian form of ${\chi }^{\prime }$ leads to the unphysical result that $\xi$ increases with $T$. In contrast, the Lorentzian form of ${\chi }^{\prime }$ yields that $\xi$ decreases with increasing $T$ and is thus fully compatible with the experimental results.

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References in corpus (1)

• Nearly Antiferromagnetic Fermi Liquids: A Progress Report

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