Comparison of charge modulations in La$_{1.875}$Ba$_{0.125}$CuO$_4$ and YBa$_2$Cu$_3$O$_{6.6}$

Abstract: A charge modulation has recently been reported in (Y,Nd)Ba$2$Cu$_3$O${6+x}$ [Ghiringhelli {\em et al.} Science 337, 821 (2013)]. Here we report Cu $L_3$ edge soft x-ray scattering studies comparing the lattice modulation associated with the charge modulation in YBa$2$Cu$_3$O${6.6}$ with that associated with the well known charge and spin stripe order in La${1.875}$Ba${0.125}$CuO$4$. We find that the correlation length in the CuO$_2$ plane is isotropic in both cases, and is $259 \pm 9$ \AA for La${1.875}$Ba${0.125}$CuO$_4$ and $55 \pm 15$ \AA for YBa$_2$Cu$_3$O${6.6}$. Assuming weak inter-planar correlations of the charge ordering in both compounds, we conclude that the order parameters of the lattice modulations in La${1.875}$Ba${0.125}$CuO$4$ and YBa$_2$Cu$_3$O${6.6}$ are of the same order of magnitude.