Coupling of stripes to lattice distortions in cuprates and nickelates

In recent X-ray diffraction experiments on orthorhombic nickelates, we have observed a significant coupling between the stripe correlations and the lattice distortion. In particular, the diagonal charge stripes of this insulating material exhibit a preferred orientation parallel to the orthorhombic a-axis, similar to the diagonal spin stripes in La2-xSrxCuO4 below the metal-insulator transition. In the light of this finding, we draw a comparison between the lightly doped parts of the phase diagrams of La2-xSrxCuO4 with low-temperature orthorhombic (LTO) structure, and La1.8-xEu0.2SrxCuO4 with low-temperature tetragonal (LT-F) structure. In La1.8-xEu0.2SrxCuO4, a local minimum in the Sr dependence of the LTO/LTT transition temperature, as well as reduced spin-glass transition temperatures, may be indicators for the presence of diagonal charge correlations. Above the metal-insulator transition the LTT phase is suited to pin parallel stripes, while below that transition the LTT phase seems instead to compete with the formation of diagonal stripes. (c) 2007 Elsevier B.V. All rights reserved.