Florian Gebhard

MULTIBAND GUTZWILLER WAVE FUNCTIONS FOR GENERAL ON-SITE INTERACTIONS

We introduce Gutzwiller wave functions for multi-band models with general on-site Coulomb interactions. As these wave functions employ correlators for the exact atomic eigenstates they are exact both in the non-interacting and in the atomic limit. We evaluate them in infinite lattice dimensions for all interaction strengths without any restrictions on the structure of the Hamiltonian or the symmetry of the ground state. The results for the ground-state energy allow us to derive an effective one-electron Hamiltonian for Landau quasi-particles, applicable for finite temperatures and frequencies within the Fermi-liquid regime. As applications for a two-band model we study the Brinkman-Rice metal-to-insulator transition at half band-filling, and the transition to itinerant ferromagnetism for two specific fillings, at and close to a peak in the density of states of the non-interacting system. Our new results significantly differ from those for earlier Gutzwiller wave functions where only density-type interactions were included. When the correct spin symmetries for the two-electron states are taken into account, the importance of the Hunds-rule exchange interaction is even more pronounced and leads to paramagnetic metallic ground states with large local magnetic moments. Ferromagnetism requires fairly large interaction strengths, and the resulting ferromagnetic state is a strongly correlated metal.

Excited states of ladder-type poly- p -phenylene oligomers

The ground-state properties and excited states of ladder-type paraphenylene oligomers are calculated applying semiempirical methods for up to 11 phenylene rings. The results are in qualitative agreement with experimental data. A scheme to interpret the excited states is developed which reveals the excitonic nature of the excited states. The electron-hole pair of the

Tomonaga-Luttinger parameters for doped Mott insulators

{S}_{1}

Spectral Function of the One-Dimensional Hubbard Model away from Half Filling

state has a mean distance of approximately

Optical conductivity of the half-filled hubbard chain

4 \AA{}.

Effect of electric field on diffusion in disordered materials. II. Two- and three-dimensional hopping transport

The Tomonaga-Luttinger parameter Kρ determines the critical behavior in quasi–one-dimensional correlated electron systems, e.g., the exponent α for the density of states near the Fermi energy. We use the numerical density-matrix renormalization group method to calculate Kρ from the slope of the density-density correlation function in momentum space at zero wave vector. We check the accuracy of our new approach against exact results for the Hubbard and XXZ Heisenberg models. We determine Kρ in the phase diagram of the extended Hubbard model at quarter filling, nc = 1/2, and confirm the bosonization results Kρ = nc2 = 1/4 on the critical line and KρCDW = nc2/2 = 1/8 at infinitesimal doping of the charge-density-wave (CDW) insulator for all interaction strengths. The doped CDW insulator exhibits exponents α > 1 only for small doping and strong correlations.

Gutzwiller theory of band magnetism in LaOFeAs.

We calculate the photoemission spectral function of the one-dimensional Hubbard model away from half filling using the dynamical density-matrix renormalization group method. An approach for calculating momentum-dependent quantities in finite open chains is presented. Comparison with exact Bethe ansatz results demonstrates the unprecedented accuracy of our method. Our results show that the photoemission spectrum of the quasi-one-dimensional conductor TTF-TCNQ provides evidence for spin-charge separation on the scale of the conduction bandwidth.

Fourth-order perturbation theory for the half-filled Hubbard model in infinite dimensions

We combine well-controlled analytical and numerical methods to determine the optical conductivity of the one-dimensional Mott-Hubbard insulator at zero temperature. A dynamical density-matrix renormalization group method provides the entire absorption spectrum for all but very small coupling strengths. In this limit we calculate the conductivity analytically using exact field-theoretical methods. Above the Lieb-Wu gap the conductivity exhibits a characteristic square-root increase. For small to moderate interactions, a sharp maximum occurs just above the gap. For larger interactions, another weak feature becomes visible around the middle of the absorption band.

Variational evaluation of correlation functions for lattice electrons in high dimensions

Abstract In this, the last of three articles on the optical absorption of electrons in a half-filled Peierls-distorted chain, we address the dimerized extended Hubbard model in the limit of a large on-site interaction U. When the Hubbard interaction is large compared with both the bandwidth W and the nearest-neighbour interaction V, the charge dynamics are properly described by the Harris-Lange model. This model can be exactly mapped onto a model of free spinless fermions in parallel (Hubbard) bands of width W which are eventually Peierls split. To determine the coherent absorption features at low temperatures, we design and employ the ‘no-recoil approximation’ in which we assume that the momentum transfer to the spin degrees of freedom can only be Δqs = 0 or Δqs = π/a during an optical excitation. We present explicit analytical results for the optical absorption in the presence of a lattice dimerization δ and a nearest-neighbour interaction V for the Neel and dimer state. We find that the coherent part o...