Orbital selective Mott transition in 3D and 5F materials

Abstract

OF THE DISSERTATION Orbital selective Mott transition in 3d and 5f materials by Antonina Toropova Dissertation Director: Professor Gabriel Kotliar We study two types of strongly correlated electron systems in the example of the transition oxide CrO2 and actinide series. We found that the physics of both types of materials can be interpreted and discussed using concept of orbital selective Mott transition (OSMT). The theory of OSMT is discussed in framework of the multiorbital Hubbard model applied to the description of t2g orbitals of Cr atoms in chromium dioxide as well as in the framework of a more generalized model for 5f materials containing both Hubbard-like and Anderson-like contributions. The electronic structure, transport, and magnetic properties of selected compounds are investigated by means of Ab Initio calculations. The many body techniques such as LDA+U and dynamical mean field theory (DMFT) have been used in addition to density functional based local density approximation (LDA) method. The half-metallic ferromagnet CrO2 has been shown to demonstrate effectively weakly correlated behavior in ordered state due to big exchange splitting within t2g orbitals. The detailed DMFT study with Quantum Monte Carlo (QMC) impurity solver revealed that in the paramagnetic state this compound was on the edge of a quantum transition. In the case of the actinide series we first demonstrated the choice of basis which optimum for DMFT based calculations. By means of detailed one-electron band structure analysis we showed that hybridization term of 5f -orbitals with conduction electrons must be included in the actinide Hamiltonian due to permanent presence of uncorrelated states at Fermi level. We conclude study of 5f -materials presenting tight-binding parametrization and exploring magnetic characteristics.