X-ray diffraction study of charge stripe order in La$_{1.875-x}$Ba$_{0.125-x}$Sr$_{x}$CuO$_{4}$

The charge stripe order in La$_{1.875-x}$Ba$_{0.125- x}$Sr$_{x}$CuO$_{4}$ with $0.05\leq x\leq 0.10$ and its relevance with high-$T_{\rm c}$ superconductivity have been investigated by synchrotron X-ray diffraction. For $x=0.05$, as temperature decreases, incommensurate superlattice peaks associated with the stripe order appear just below the structural phase transition temperature $T_{\rm d2}$, indicating the strong relevance between the formation of the charge stripe order and the structural phase transition. However, in $x=0.075$ and 0.09, the superlattice peaks emerge far above $T_{\rm d2}$ as a short range correlation, indicating a precursor of charge ordering. Furthermore, temperature dependences of the superlattice peak intensity, correlation length, and incommensurability for $x=0.05$ are different from those for $x=0.075$ and 0.09. These results suggest that the transition process into the charge stripe order strongly correlates with the order of the structural phase transitions. A quantitative comparison of the structure factor associated with the charge order have been also made for all the samples.