Charge stripes and spin correlations in copper-oxide superconductors

摘要

To obtain superconductivity in a layered copper-oxide compound, it is necessary to introduce charge carriers into the antiferromagnetic CuO(sub 2) planes. Recent neutron diffraction studies of the system La(sub 1.6-x)Nd(sub 0.4)Sr(sub x)CuO(sub 4) 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 La(sub 2)NiO(sub 4). 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 La(sub 2-x)Sr(sub x)CuO(sub 4), the magnetic scattering that is observed is purely inelastic. 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. 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 to pinning of the otherwise dynamic correlations by a special distortion of the lattice. That distortion is driven by purely ionic interactions and is stabilized by the smaller ionic radius of the substituted Nd.