Glassy slowing of stripe modulation in (La,Eu,Nd)(2-x)(Sr,Ba)(x)CuO4: A Cu-63 and La-139 NQR study down to 350 mK - art. no. 134525 [Review]

摘要

Cu-63 and La-139 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)(y)SrxCuO4. The first goal of the present study is to utilize the fact that ordered Cu magnetic moments exert a static hyperfine field on the Cu-63 and La-139 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 approximate to1/8. Detailed numerical analysis of the Cu-63 NQR line shape establishes that widely accepted models of periodic sinusoidal or square-well-shaped modulations of spin density waves with maximum moment similar to0.3 mu (B), as inferred from elastic neutron scattering and muon spin rotation (mu SR) measurements. cannot account for the NQR line shape unless we assume a relatively small ordered moment similar to0.15 mu (B) 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 Cu-63 NQR intensity below charge ordering temperature T-charge 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 Cu-63 and La-139 NQR, the spin order parameter measured by elastic neutron scattering, and the mu SR data, we deduce the spatial distribution of the spin fluctuation frequency scale Gamma 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 2 pi rho (eff)(s) similar to 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. [References: 112]