02 Mars – Thesis defense - Bishal Poudel

14 h Amphi D - building A29 (University of Bordeaux | Talence campus)

Lattice coherence and local non-local duality in f-electron materials.

In this thesis, we will study f-electron systems under two different aspects: the formation and the breakdown of lattice coherence, and the nature of f-electrons, which can be either localized, itinerant, or dual. In the first part, we study lattice coherence in 4f systems with the atomic substitution of magnetic atoms by non-magnetic atoms. We will deal with the substitutional disorder by using the dynamic mean-field, theory. We start by generalizing the Doniach type phase diagram with substitution by considering the phases: ferromagnetic, antiferromagnetic, and paramagnetic Kondo. We also study the relevance of our phase diagrams by comparing the experimental data of various cerium-based Kondo alloys. Next, we will focus on the Kondo paramagnetic phase on a square lattice in order to study the signatures of lattice coherence breakdown with the dilution of magnetic impurities. To do this, we analyze the photoemission signals, the effective masses, the local potential scattering, and the charge order. We confirmed previous predictions of a Lifshitz-type transition between dilute and dense impurity systems. In addition, we detect a new critical concentration where the quasiparticle effective mass cancels out. The second part of this thesis deals with the dual character of 5f electrons: itinerant and localized at the same time. To study this duality, we use the method rotationally invariant slave-bosons on UPt3. By varying the anisotropies over the electronic bandwidths, we study the possibility of having orbital selective partially localized phases, and we construct a phase diagram. Finally, we analyze the different partially localized phases in terms of orbital-dependent quasiparticle mass and occupation, magnetization, and valency configurations.

Event localization