63,65Cu nuclear quadrupole resonance study of YBa2(Cu1−xNix)3O7−δ

Tcreduction in Sr-substitutedY(Ba1−xYing1, Li2, Liu3 et al. 2002Phys. Rev. B10020View full textAdd to dashboardCite

“…The spectrum of undoped YBa 2 Cu 3 O 7Ϫ␦ in this range mainly shows two NQR peaks at 31.20 and 28.87 MHz, which have been assigned to 63 Cu(2) and 65 Cu(2) in the CuO 2 plane, respectively. We note that 31.20 MHz 63 Cu(2) peak has a trace of small peak around 30 MHz, which has been observed elsewhere [17][18][19] and attributed to the Cu NQR signals accompanying the local lower oxygen content. 18 During the Sr substitution, the 63,65 Cu(2) NQR spectra are shifted toward higher frequencies and linewidths increase, and a new Cu NQR shoulder peak appears at the lower frequency side of the Cu͑2͒ signal.…”

“…[20][21][22][23][24] At the same time, some theoretical and experimental results show that carrier density dependence of NQR frequency Q is also roughly valid for the fourfold coordinated Cu͑1͒ site. 17,24,25 With Sr substitution in Y123, the planar Cu͑2͒ NQR spectra are shifted to higher frequencies, and the chain Cu͑1͒ NQR spectra are shifted to lower frequencies, which is similar to the case for Sr substituted Y124. 16 This result of NQR frequency Q shift suggests that holes increase on the Cu͑2͒ site and decrease on the Cu͑1͒ site.…”