Glassy spin freezing and NMR wipeout effect in the high-Tc superconductor La1.90Sr0.10CuO4:: Critical discussion of the role of stripes -: art. no. 144508

We report on La-139 and Cu-63 NMR/NQR measurements in the high-T-c superconductor La1.90Sr0.10CuO4, with T-c=26.5 K. Spin fluctuations probed by La-139 spin-lattice relaxation (T-1) continuously slow down on cooling through T-c. We argue that spin freezing and superconductivity are bulk effects in this sample. Thus both phenomena have to coexist microscopically. The distribution of La-139 T-1 values at low temperature reveals a wide spread of spin fluctuation frequencies in CuO2 planes. A simple estimate shows that Cu-63 nuclei at sites where electronic fluctuations are the slowest are not observable (wipeout effect) because relaxation times are too short. This means that the Cu-63 NQR wipeout, observed in this sample, can be explained primarily by slow magnetic, rather than charge, fluctuations. The magnetic origin of the wipeout is still compatible with a connection between wipeout and charge order [as proposed by Hunt et al., Phys. Rev. Lett. 82, 4300 (1999)], but this connection is indirect. On the other hand, since the wipeout fraction is not an intensive quantity it cannot define a proper order parameter and cannot be used by itself as a criterion for the existence of a stripe phase.