Cu63NMR shift and linewidth anomalies in theTc=60 K phase of Y-Ba-Cu-O

Abstract

${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ NMR shifts and spectra are presented for both Cu(1) and Cu(2) sites in a specimen of ${\mathrm{YBa}}_{\mathit{z}}$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.64}$ (${\mathit{T}}_{\mathit{c}}$∼60 K). For H along the c axis, the Cu(2) shift is not distinguishable from that reported for ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7.0}$. For H in the a-b plane, the spin component of Cu(2) shift declines sharply as T→${\mathit{T}}_{\mathit{c}}$. The Cu(1) shift behaves similarly, showing also a dramatic broadening at low temperatures in clearly nonmetallic behavior. Combined with anomalous ${\mathit{T}}_1$ data reported earlier for the 60-K phase of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6+\mathit{x}}$, these results are shown to be consistent with strong and monotonically increasing antiferromagnetic correlations as T is decreased.