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Angle-resolved photoemission studies on Sr 2 CuO 2 Cl 2 at a temperature below its Néel temperature reveal detailed momentum dependent line shape changes as a function of wave vector. While a sharp quasiparticlelike peak is observed near (p͞2, p͞2), broad peaks are observed near (p, 0). Additional second and third neighbor hopping terms must be added to the t-J Hamiltonian to account for both the dispersion and the line shape. It is found that this Hamiltonian can be used to explain the measured momentum dependent spectral function for hole-doped materials, both underdoped and overdoped, as well as electron-doped materials. [S0031-9007(98)06100-6]

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The electronic structure of La0.7Ce0.3MnO3 (LCeMO) has been investigated by using photoemission spectroscopy. A very weak 4f resonance is observed and the Ce 3d spectrum of LCeMO is very similar to that of CeO2, indicating that Ce ions are far from being trivalent. The Mn 2p core-level spectrum of LCeMO is essentially the same as that of hole-doped La0.7Sr0.3MnO3, but different from that of MnO. The local spin-density approximation (LSDA) electronic structure calculations for LCeMO show that the Mn 3d states contribute a large peak around -2 eV and a weak structure between -2 eV and EF, and that the O 2p states are spread between -3 eV and -9 eV, with negligible contribution near EF. The LSDA calculations for LCeMO and hole-doped La0.7Ba0.3MnO3 reveal that the calculated Mn 3d density of states at EF in LCeMO is larger, reflecting the effect of electron doping with Ce ions.

In this paper, we discuss neutron and synchrotron x-ray diffraction data obtained from single crystals of ACr2O4 (A = Zn, Cd). The Cr spinels undergo three-dimensional spin-Peierls transitions at low temperatures that involve cubic-to-tetragonal lattice distortions and magnetic long-range ordering. Our results show that the magnetic structures selected by these systems are closely related to the lattice distortions that are undertaken.