Electronic correlation and transport phenomena in Mott and Kondo materials

Abstract

Strong electronic correlation effects are at the heart of a plethora of physical phenomenain materials at the forefront of condensed-matter research.Understanding the correlated electronic state and its modification by external stimuli, including the emergence of collective excitations, areamong the leading topics of interest these days.The present thesis concerns itself with two distinct types of material classes: (i) systems where, through strong electron interactions, the effects of Mott localization are prevalent and (ii) systems where the magnetic coupling of local moments leads to signatures of the (lattice) Kondo effect.As the emerging characteristics of these materials are, per definition, beyond a free-particle picture, it is necessary to first introduce an appropriate quantum-field theoretical description of the many-body problem.Then, the first part of this thesis will mainly focus on the transition-metal oxide SrVO3:Motivated by recent experiments that employ epitaxial growth methods, we scrutinize the, for Mott materials characteristic, observed metal-insulator transitions.With the help of dynamical mean-field theory (and beyond) the corresponding one- and two-particle propagators, encoding the prevalent correlations effects, are analyzed.These insights allow us to characterize spectral properties, quantum fluctuations and transport coefficients alike.The second part of this thesis focuses on the emergent correlation phenomena in the cerium-based Kondo insulator Ce3Bi4Pt3.By comparison with the prototypical periodic Anderson model, we scrutinize the crystal structure, its correlated electronic state, and the reason why hydrostatic pressure leads to a non-canonical behavior in experiment.From there, a candidate mechanism is developed that supports the phenomenon of resistivity saturation both in Ce3Bi4Pt3 and other related hybridization-gap insulators.Based on the same underlying premise of lifetime effects, all higher order transport kernels, that build the foundation of thermoelectric and magnetoelectric transport coefficients, are derived and benchmarked.To assess the general validity of this formalism, it is applied on a wider range of models and realistic crystal structures. Furthermore we make the developed methodology available in the form of an open source program package.