Analytical ground state for the three-band Hubbard model

For the calculation of charge excitations as those observed in, e.g., photo-emission spectroscopy or in electron-energy loss spectroscopy, a correct description of ground-state charge properties is essential. In strongly correlated systems like the undoped cuprates this is a highly non-trivial problem. In this paper we derive a non-perturbative analytical approximation for the ground state of the three-band Hubbard model on an infinite, half filled CuO_2 plane. By comparison with Projector Quantum Monte Carlo calculations it is shown that the resulting expressions correctly describe the charge properties of the ground state. Relations to other approaches are discussed. The analytical ground state preserves size consistency and can be generalized for other geometries, while still being both easy to interpret and to evaluate.Comment: REVTeX, 8 pages, 6 figures, to appear in Phys. Rev.

Realistic description of electron-energy loss spectroscopy for One-Dimensional Sr2_2CuO3_3

We investigate the electron-energy loss spectrum of one-dimensional undoped CuO$_{3}$ chains within an extended multi-band Hubbard model and an extended one-band Hubbard model, using the standard Lanczos algorithm. Short-range intersite Coulomb interactions are explicitly included in these models, and long-range interactions are treated in random-phase approximation. The results for the multi-band model with standard parameter values agree very well with experimental spectra of Sr$_{2}$CuO$_{3}$. In particular, the width of the main structure is correctly reproduced for all values of momentum transfer. It is shown for both models that intersite Coulomb interactions mainly lead to an energy shift of the spectra. We find no evidence for enhanced intersite interactions in Sr$_{2}$CuO$_{3}$.Comment: 4 pages, 4 figure

The dynamics of a hole in a CuO_4 plaquette: electron energy-loss spectroscopy of Li_2CuO_2

We have measured the energy and momentum dependent loss function of Li_2CuO_2 single crystals by means of electron energy-loss spectroscopy in transmission. Using the same values for the model parameters, the low-energy features of the spectrum as well as published Cu 2p_(3/2) x-ray photoemission data of Li_2CuO_2 are well described by a cluster model that consists of a single CuO_4 plaquette only. This demonstrates that charge excitations in Li_2CuO_2 are strongly localized.Comment: 5 pages, 5 figure

One-dimensional dynamics of the d-electrons in α′\alpha'-NaV2_{2}O5_{5}

We have studied the electronic properties of the ladder compound $\alpha'$-NaV$_{2}$O$_{5}$, adopting a joint experimental and theoretical approach. The momentum-dependent loss function was measured using electron energy-loss spectroscopy in transmission. The optical conductivity derived from the loss function by a Kramers-Kronig analysis agrees well with our results from LSDA+U band-structure calculations upon application of an antiferromagnetic alignment of the V~3$d_{xy}$ spins along the legs and an on-site Coulomb interaction U of between 2 and 3 eV. The decomposition of the calculated optical conductivity into contributions from transitions between selected energy regions of the DOS reveals the origin of the observed anisotropy of the optical conductivity. In addition, we have investigated the plasmon excitations related to transitions between the vanadium states within an effective 16 site vanadium cluster model. Good agreement between the theoretical and experimental loss function was obtained using the hopping parameters derived from the tight binding fit to the band-structure and moderate Coulomb interactions between the electrons within the ab plane.Comment: 23 pages, 8 figures; submitted to PR

Charge properties of cuprates: ground state and excitations

This thesis investigates charge properties of undoped cuprate compounds. We develop a new analytical approach to the approximation of ground-state charge properties and apply it to the geometries found in the cuprates. With the additional help of numerical methods (Projector Quantum Monte Carlo) we analyze the influence of the dimensionality on the ground state properties. A further topic are charge excitations, especially Cu 2p_3_/_2 core-level X-ray photoemission spectroscopy (XPS). Low dimensional systems are treated with exactly solvable models, which allow a good description of experimental data. For systems of higher dimensionality an approximation scheme using projection technique is presented. The results are compared to several experimental spectra.SIGLEAvailable from: http://hsss.slub-dresden.de/pub2/disseration/2001/mathematik / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Hidden Assumptions in the Dutch Book Argument

Dutch Book argument, degree of belief, probability, coherence, probabilistic theories of rationality,