Glassy slowing of stripe modulation in (La,Eu,Nd)2-x(Sr,Ba)xCuO4: A 63Cu and 139La NQR study down to 350 mK

⁶³Cu and ¹³⁹La nuclear quadrupole resonance and Zeeman perturbed nuclear magnetic resonance experiments are performed on the striped phase of the high-temperature superconductors La2-xBaxCuO4 and La2-x-y(Nd,Eu)ySrxCuO4. The first goal of the present study is to utilize the fact that ordered Cu magnetic moments exert a static hyperfine field on the ⁶³Cu and ¹³⁹La nuclei to deduce the charge density and ordered moment within the CuO2 planes. A hyperfine-broadened nuclear quadrupole resonance (NQR) line shape is observed in both La2-xBaxCuO4 and La1.80-xEu0.20SrxCuO4 for x≈1/8. Detailed numerical analysis of the ⁶³Cu NQR line shape establishes that widely accepted models of periodic sinusoidal or square-well-shaped modulations of spin density waves with maximum moment ∼0.3 μB, as inferred from elastic neutron scattering and muon spin rotation (μ SR) measurements, cannot account for the NQR line shape unless we assume a relatively small ordered moment ∼0.15 μB with a comparably large distribution. The second goal of the present work is to establish the temperature dependence of the fluctuation frequency scale of stripes. We find that the fraction of missing ⁶³Cu NQR intensity below charge ordering temperature Tcharge accurately tracks the temperature dependence of the charge order parameter as measured by scattering methods. By fitting a single model to the temperature dependences of the wipeout fraction F(T) for ⁶³Cu and ¹³⁹La NQR, the spin order parameter measured by elastic neutron scattering, and the μSR data, we deduce the spatial distribution of the spin fluctuation frequency scale Γ and its temperature dependence, These results indicate that as soon as the charge dynamics slow down, the spin fluctuations begin to slow dramatically with spin stiffness 2πρs^eff ∼ 200 K. By extending the analysis to other hole concentrations, we demonstrate a qualitative difference in the spatial variation of electronic states induced by slowing the charge dynamics above and below x=1/8.