Charge stripes and spin correlations in copper-oxide superconductors

To obtain superconductivity in a layered copper-oxide compound, it is necessary to introduce charge carriers into the antiferromagnetic CuO2 planes. Recent neutron diffraction studies of the system La1.6−xNd0.4SrxCuO4 [1,2] provide evidence that the dopant-induced holes choose to segregate into periodically-spaced stripes which separate antiferromagnetic domains, in a manner similar to that found in hole-doped La2NiO4 [3]. The charge and spin stripe modulations are identified by the appearance of scattering at incommensurate positions. In the Nd-doped system, elastic scattering is observed, corresponding to static stripes. In pure La2−xSrxCuO4, the magnetic scattering that is observed is purely inelastic [4]. Where samples with and without Nd, but with the same Sr concentration, have been measured, the incommensurate (IC) splittings of the magnetic signal are found to be essentially identical [2,4,5]. It has been proposed that the spin correlations in the two systems are fundamentally the same, thus implying similar charge correlations. The static nature of the stripes in the Nd-doped system is attributed [1] to pinning of the otherwise dynamic correlations by a special distortion of the lattice [6]. That distortion is driven by purely ionic interactions and is stabilized by the smaller ionic radius of the substituted Nd. To strengthen the case for the charge-stripe in-