The k-dependent electronic structure of the low temperature ferromagnetic state of La 1.2 Sr 1.8 Mn 2 O 7 was measured using angle-resolved photoemission spectroscopy and calculated using the local spin density approximation (LSDA). The measured near-Fermi energy states display E vs k and symmetry relationships which agree relatively well with the LSDA prediction through much of the Brillouin zone, and the locus of lowest energy excitations matches the predicted large Fermi surface quite well. However, the spectral features are too broad to be well described as Fermi-liquid-like quasiparticles, and they are strongly suppressed from the Fermi energy, i.e., there is a pseudogap in the excitation spectrum. We discuss the spectral properties in terms of strong coupling to a local effect such as a lattice distortion. [S0031-9007(98)06522-3]

Angle-resolved photoemission studies of the dispersion relations and polarization dependence of bands in the near E F region of untwinned YBa 2 Cu 3 O 7Ϫ␦ ͑Y123͒ single crystals reveal previously unseen details of the electronic structure and significantly expand our understanding of this system. We find that the narrow, intense feature seen along ⌫Y in Y123 and YBa 2 Cu 4 O 8 ͑Y124͒ is best explained as a surface termination effect related to the quasi-one-dimensional CuO 3 chains, masking underlying electronic states at the Fermi energy. Many of the previously puzzling photoemission results from these materials are readily understood within this context, including the failure to observe a superconducting gap, the weak effect of deoxygenation on the photoemission spectra for ␦р0.5, the weak dependence of this feature on Pr doping, and the strong photon energy dependence of the photoemission spectra. Our data, taken in the superconducting state, reveal the bilayer splitting and c-axis dispersion of the CuO 2 plane bands. We also find evidence for a one-dimensional chain Fermi surface parallel to the ⌫X direction, but see no indication of the BaO derived ''stick'' pocket centered on the S point. ͓S0163-1829͑98͒04910-8͔

We present complete Fermi-surface mappings of an untwinned single crystal of YBa 2 Cu 3 O 7Ϫ␦ in two distinct photon polarization geometries. Various methods for Fermi-surface determination with angle-resolved photoelectron spectroscopy are discussed and a technique based on the momentum space density of states is developed and applied. The data reveal the presence of two CuO 2 plane-derived Fermi-surface pockets, along with weak evidence for a single chain sheet, in agreement with earlier work on twinned crystals and ab initio predictions, but show no sign of the expected ''stick'' pocket centered at (,). In contrast with earlier work on Bi 2 Sr 2 CaCu 2 O 8ϩ␦ , we see no evidence for ''shadow bands'' in optimally doped YBa 2 Cu 3 O 7Ϫ␦ , supporting the contention that these features arise from structural rather than magnetic correlations.