The charge ordering in the bilayer manganite system La 2−2x Sr 1+2x Mn 2 O 7 with 0.30 ≤ x ≤ 0.50 has been studied by neutron diffraction. The charge order is characterized by the propagation vector parallel to the [1 0 0] direction ( MnO 2 direction), but the correlation length is short-ranged and extremely anisotropic, being ∼ 0.02a * and ∼ 0.2a * parallel and perpendicular to the modulation direction, respectively.The observed charge order can be viewed as a quasi-bi-stripe order, and accounts well for the x dependence of the resistivity. The quasi-bistripe order is stable within the ferromagnetic (FM) MnO 2 layers in the A-type antiferromagnetic order, but is instabilized by the 3 dimensional FM order.
The electronic structures of the nearly optimally doped single-layer, bilayer and trilayer Bi-based cuprates are investigated by angle-resolved photoemission spectroscopy. A lineshape analysis of data taken for different photon energies indicates that the interlayer coupling within the trilayer is not stronger than its counterpart in the bilayer system. This suggests that the higher T c of the trilayer cuprate superconductors is not due to an enhancement of the coupling strength between the neighboring CuO2 planes within each unit cell.
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