Doping dependent quasiparticle band structure in cuprate superconductors

We present an exact diagonalization study of the single particle spectral function in the so-called t-t'-t''-J model in 2D. As a key result, we find that unlike the `pure' t-J model, hole doping leads to a major reconstruction of the quasiparticle band structure near (pi,0): whereas for the undoped system the quasiparticle states near (pi,0) are deep below the top of the band at (pi/2,pi/2), hole doping shifts these states up to E_F, resulting in extended flat band regions close to E_F and around (pi,0). This strong doping-induced deformation can be directly compared to angle resolved photoemission results on Sr_2 Cu Cl_2 O_2, underdoped Bi2212 and optimally doped Bi2212. We propose the interplay of long range hopping and decreasing spin correlations as the mechanism of this deformation.Comment: 4 pages, Revtex, with 4 embedded eps figures. Hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to [email protected]

Charged excitons in doped extended Hubbard model systems

We show that the charge transfer excitons in a Hubbard model system including nearest neighbor Coulomb interactions effectively attain some charge in doped systems and become visible in photoelectron and inverse photoelectron spectroscopies. This shows that the description of a doped system by an extended Hubbard model differs substantially from that of a simple Hubbard model. Longer range Coulomb interactions cause satellites in the one electron removal and addition spectra and the appearance of spectral weight if the gap of doped systems at energies corresponding to the excitons of the undoped systems. The spectral weight of the satellites is proportional to the doping times the coordination number and therefore is strongly dependent on the dimension.Comment: 10 pages revtex, 5 figures ps figures adde

Does EELS haunt your photoemission measurements?

It has been argued in a recent paper by R. Joynt (R. Joynt, Science 284, p 777 (1999)) that in the case of poorly conducting solids the photoemission spectrum close to the Fermi Energy may be strongly influenced by extrinsic loss processes similar to those occurring in High Resolution Electron Energy Loss Spectroscopy (HR-EELS), thereby obscuring information concerning the density of states or one electron Green's function sought for. In this paper we present a number of arguments, both theoretical and experimental, that demonstrate that energy loss processes occurring once the electron is outside the solid, contribute only weakly to the spectrum and can in most cases be either neglected or treated as a weak structureless background.Comment: 6 pages, figures included. Submitted to PR

Single polaron properties of the breathing-mode Hamiltonian

We investigate numerically various properties of the one-dimensional (1D) breathing-mode polaron. We use an extension of a variational scheme to compute the energies and wave-functions of the two lowest-energy eigenstates for any momentum, as well as a scheme to compute directly the polaron Greens function. We contrast these results with results for the 1D Holstein polaron. In particular, we find that the crossover from a large to a small polaron is significantly sharper. Unlike for the Holstein model, at moderate and large couplings the breathing-mode polaron dispersion has non-monotonic dependence on the polaron momentum k. Neither of these aspects is revealed by a previous study based on the self-consistent Born approximation

Non-resonant inelastic x-ray scattering involving excitonic excitations

In a recent publication Larson \textit{et al.} reported remarkably clear $d$-$d$ excitations for NiO and CoO measured with x-ray energies well below the transition metal $K$ edge. In this letter we demonstrate that we can obtain an accurate quantitative description based on a local many body approach. We find that the magnitude of $\vec{q}$ can be tuned for maximum sensitivity for dipole, quadrupole, etc. excitations. We also find that the direction of $\vec{q}$ with respect to the crystal axes can be used as an equivalent to polarization similar to electron energy loss spectroscopy, allowing for a determination of the local symmetry of the initial and final state based on selection rules. This method is more generally applicable and combined with the high resolution available, could be a powerful tool for the study of local distortions and symmetries in transition metal compounds including also buried interfaces

High multipole transitions in NIXS: valence and hybridization in 4f systems

Momentum-transfer (q) dependent non-resonant inelastic x-ray scattering measurements were made at the N4,5 edges for several rare earth compounds. With increasing q, giant dipole resonances diminish, to be replaced by strong multiplet lines at lower energy transfer. These multiplets result from two different orders of multipole scattering and are distinct for systems with simple 4f^0 and 4f^1 initial states. A many-body theoretical treatment of the multiplets agrees well with the experimental data on ionic La and Ce phosphate reference compounds. Comparing measurements on CeO2 and CeRh3 to the theory and the phosphates indicates sensitivity to hybridization as observed by a broadening of 4f^0-related multiplet features. We expect such strong, nondipole features to be generic for NIXS from f-electron systems

Geologic and mineral and water resources investigations in western Colorado, using Skylab EREP data

The author has identified the following significant results. Skylab photographs are superior to ERTS images for photogeologic interpretation, primarily because of improved resolution. Lithologic contacts can be detected consistently better on Skylab S190A photos than on ERTS images. Color photos are best; red and green band photos are somewhat better than color-infrared photos; infrared band photos are worst. All major geologic structures can be recognized on Skylab imagery. Large folds, even those with very gentle flexures, can be mapped accurately and with confidence. Bedding attitudes of only a few degrees are recognized; vertical exaggeration factor is about 2.5X. Mineral deposits in central Colorado may be indicated on Skylab photos by lineaments and color anomalies, but positive identification of these features is not possible. S190A stereo color photography is adequate for defining drainage divides that in turn define the boundaries and distribution of ground water recharge and discharge areas within a basin

Non conventional screening of the Coulomb interaction in low dimensional and finite size system

We study the screening of the Coulomb interaction in non polar systems by polarizable atoms. We show that in low dimensions and small finite size systems this screening deviates strongly from that conventionally assumed. In fact in one dimension the short range interaction is strongly screened and the long range interaction is anti-screened thereby strongly reducing the gradient of the Coulomb interaction and therefore the correlation effects. We argue that this effect explains the success of mean field single particle theories for large molecules.Comment: 4 pages, 5 figure