arXiv subjects
Publications and source records attributed to Gertrud Zwicknagl.
A topical overview on the state of the art and science of superconducting materials is presented. The relation of atomic structure and suggested superconductivity mechanisms as well as possible applications are discussed for the various families of superconducting materials discovered within the last 25 years.
In this review article we present a survey of unconventional superconductors and their coexistence behaviour with magnetism. We focus on Ce- and U-based heavy fermion superconductors, in addition we discuss the rare earth borocarbide and skutterudite superconductors. We show that heavy fermion behaviour in Ce- and U- compounds should be described differently. While the Kondo-lattice model with localised 4f-electrons is appropriate for Ce-compounds, dual models including localised and itinerant 5f-electrons are necessary for U-compounds. We demonostrate that this leads to consistent results for Fermi surface topology and mass enhancement in various U-compounds. We also show that virtual exchange of localised 5f-electron excitations provides a new mechanism for unconventional superconductivity in addition to the known itinerant spin-fluctuation exchange mechanism. We discuss symmetry properties and coexistence of unconventional superconducting and density wave (hidden) order parameters and methods for their detection, notably the new angle resolved magntetotransport methods. The latter have been very succesful for the investigtion of gap anisotropies in the nonmagnetic borocarbide superconductors. Recent results on the new multiphase Pr-skutterudite superconductor are also reviewed.
We extend a recently introduced semiclassical approach to calculating the influence of local lattice fluctuations on electronic properties of metals and metallic molecular crystals. The effective action of electrons in degenerate orbital states coupling to Jahn-Teller distortions is derived, employing dynamical mean-field theory and adiabatic expansions. We improve on previous numerical treatments of the semiclassical action and present for the simplifying Holstein model results for the finite temperature optical conductivity at electron-phonon coupling strengths from weak to strong. Significant transfer of spectral weight from high to low frequencies is obtained on isotope substitution in the Fermi-liquid to polaron crossover regime.