Tobias Schickling

Gutzwiller theory of band magnetism in LaOFeAs.

We use the Gutzwiller variational theory to calculate the ground-state phase diagram and quasiparticle bands of LaOFeAs. The Fe3d-As4p Wannier-orbital basis obtained from density-functional theory defines the band part of our eight-band Hubbard model. The full atomic interaction between the electrons in the iron orbitals is parametrized by the Hubbard interaction U and an average Hunds-rule interaction J. We reproduce the experimentally observed small ordered magnetic moment over a large region of (U,J) parameter space. The magnetically ordered phase is a stripe spin-density wave of quasiparticles.

Variational study of Fermi surface deformations in Hubbard models

We study the correlation-induced deformation of Fermi surfaces by means of a new diagrammatic method which allows for the analytical evaluation of Gutzwiller wave functions in finite dimensions. In agreement with renormalization-group results we find Pomeranchuk instabilities in two-dimensional Hubbard models for sufficiently large Coulomb interactions.

Antiferromagnetic order in multiband Hubbard models for iron pnictides.

We investigate multiband Hubbard models for the three iron 3d t(2g) bands and the two iron 3d e(g) bands in LaOFeAs by means of the Gutzwiller variational theory. Our analysis of the paramagnetic ground state shows that neither Hartree-Fock mean-field theories nor effective spin models describe these systems adequately. In contrast to Hartree-Fock-type approaches, the Gutzwiller theory predicts that antiferromagnetic order requires substantial values of the local Hunds-rule exchange interaction. For the three-band model, the antiferromagnetic moment fits experimental data for a broad range of interaction parameters. However, for the more appropriate five-band model, the iron e(g) electrons polarize the t(2g) electrons and they substantially contribute to the ordered moment.

Numerical minimisation of Gutzwiller energy functionals

We give a comprehensive introduction into an efficient numerical scheme for the minimisation of Gutzwiller energy functionals for multi-band Hubbard models. Our method covers all conceivable cases of Gutzwiller variational wave functions and has been used successfully in previous numerical studies.

Quasiparticle bands and structural phase transition of iron from Gutzwiller density-functional theory

We use the Gutzwiller Density Functional Theory to calculate ground-state properties and bandstructures of iron in its body-centered-cubic (bcc) and hexagonal-close-packed (hcp) phases. For a Hubbard interaction

Gutzwiller density functional theory: a formal derivation and application to ferromagnetic nickel

U=9\, {\rm eV}

Coexistence of nematic order and superconductivity in the Hubbard model

and Hunds-rule coupling

Evaluation techniques for Gutzwiller wave functions in finite dimensions

J=0.54\, {\rm eV}

Band antiferromagnetism in a two-band model for iron pnictides

we reproduce the lattice parameter, magnetic moment, and bulk modulus of bcc iron. For these parameters, bcc is the ground-state lattice structure at ambient pressure up to a pressure of

Superconductivity in the two-dimensional Hubbard model: Gutzwiller wave function solution

p_{\rm c}=41\, {\rm GPa}