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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]

The electronic states and magnetic properties for the copper oxides containing edge-sharing Cu-O chains such as Li2CuO2, La6Ca8Cu24O41 and CuGeO3 are systematically studied. The optical conductivity (!) and the temperature dependence of the magnetic susceptibility (T ) for single crystalline samples Li2CuO2 are measured as a reference system and analyzed by using the exact diagonalization method for small Cu-O clusters. It is shown that the spectral distribution of (!) is dierent between edge-sharing and corner-sharing Cu-O-Cu bonds. The charge transfer gap in edge-sharing chains is larger than that of high-T c cuprates. The exchange interaction between nearest-neighbor copper ions in edge-sharing chains J1 depends sensitively on the Cu-O-Cu bond angles. In addition to J1, the exchange interaction between next-nearest-neighbor copper ions J2 has sucient contribution to the magnetic properties. We calculate J 1 and J 2 for all the copper oxides contaning edge-sharing Cu-O chains and discuss the magnetic properties. PACS appear here. npacsfg should always be input, even if empty.

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The electronic structure of Mott insulators continues to be a major unsolved problem in physics despite more than 50 years of research. Well-developed momentum-resolved spectroscopies such as photoemission or neutron scattering cannot probe the full Mott gap. High-resolution resonant inelastic x-ray scattering revealed dispersive charge excitations across the Mott gap in a high-critical temperature parent cuprate (Ca(2)CuO(2)Cl(2)), shedding light on the anisotropy of the Mott gap. These charge excitations across the Mott gap can be described within the framework of the Hubbard model.

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How coherent quasiparticles emerge by doping quantum antiferromagnets is a key question in correlated electron systems, whose resolution is needed to elucidate the phase diagram of copper oxides. Recent resonant inelastic X-ray scattering (RIXS) experiments in hole-doped cuprates have purported to measure high-energy collective spin excitations that persist well into the overdoped regime and bear a striking resemblance to those found in the parent compound, challenging the perception that spin excitations should weaken with doping and have a diminishing effect on superconductivity. Here we show that RIXS at the Cu L 3 -edge indeed provides access to the spin dynamical structure factor once one considers the full influence of light polarization. Further we demonstrate that high-energy spin excitations do not correlate with the doping dependence of T c , while low-energy excitations depend sensitively on doping and show ferromagnetic correlations. This suggests that high-energy spin excitations are marginal to pairing in cuprate superconductors.