Photoemission response ofBi2Sr2CaCu2Ox: The normal-state anisotropy is intrinsic

Angle-resolved, synchrotron-radiation photoemission and low-energy electron-diffraction studies of single-crystal ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathit{x}}$ high-temperature superconductors establish that the [100] and [010] directions exhibit quantitatively different structural and electronic properties. Specifically, there is a superlattice modulation in the [010] direction, with superlattice period between 4.7 and 5.2 times the period in the [100] direction. Accompanying this structural difference there is a marked difference in the intensity and amount of dispersion in the two directions.