Observation of Cu NMR in antiferromagnetic ${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$: Evidence for hole-band filling

Copper nuclear magnetic resonance (NMR) has been observed at plane and chain Cu sites in ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$. The field-swept NMR signal from plane Cu sites disappears due to magnetic ordering below ∼280 K. In the antiferromagnetic state (T=1.4 K) quadrupole-split NMR spectra from plane-site Cu nuclei can be fit using an axial electric-field gradient (${\nu }_{\mathit{Q}}$=17±2 MHz) and an internal field ${\mathit{H}}_{\mathrm{int}}$=65.2±0.2 kOe directed at an angle 79°±1° to the c axis. The observation of plane-Cu magnetism is consistent with the absence of doped holes on ${\mathrm{CuO}}_2$ planes in ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$, which supports the view that hole filling is important in suppressing superconductivity in ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$.