Variational cluster approximation at finite temperatures

Abstract

Being able to describe thermodynamics and dynamics of ordered systems at finite temperature allows capturing the signatures of different phases as well as thermal transitions between them. Systems of strongly correlated electrons residing in multiple orbitals where spin-orbit coupling is of significance can exhibit a multitude of exotic phases. Modelling these systems and capturing their properties for the entire temperature range is a non-trivial task. In this thesis, the implementation details of several cluster solvers used for the variational cluster approximation (VCA) at finite temperature are described, since this method is capable of modelling the systems mentioned before while incorporating local quantum fluctuations. The most reliable, sufficiently benchmarked and best performing solver among them is then used to investigate the magnetic and orbital properties of Sr2IrO4 and Ca2RuO4 described by three-band Hubbard models, as well as the Kondo lattice model at half-filling.