This thesis reports original research on strongly interacting fermions described by Hubbardlike models which can be realized with ultracold atom experiments. In particular, two main directions have been pursued: (i) the control of magnetic and topological properties in a honeycomb lattice through a suitable tuning of the trapping potential, and (ii) the possibility to observe orbitalselective Mott physics in a multicomponent Fermi system where the SU(N) symmetry is broken in a controlled way. The first line of research is based on the idea that increasing the strength of a trapping potential, one can trap a strongly interacting fermions in a limited portion of space, thereby changing their average density and the related magnetic properties. In particular it was demonstrated that this confinement protocol can be used to designeffective “nanoflakes” which are reminiscent of a solidstate proposal [1]. The second step was to extend the same philosophy to the socalled KaneMele model, a spinful version of the paradigmatic model proposed by Haldane which presents quantum Hall states. This model can be realized with coldatom systems using artificial gauge fields. In this thesis we consider a KaneMeleHubbard model where the electronic structure of the KaneMele model is supplemented by the onsite Hubbard interaction, allowing us to study the interplay between the correlations and magnetism induced by the repulsion, with the nontrivial topological properties. Also for this model, we follow the strategy discussed above, namely the possibility to engineer an effective “nanoflake” by tuning the lattice potential. The final outcome in this case is even reacher, because it leads, among other results, to a situation where the effective flake hosts an inhomogeneous state which presents at the same time topologically nontrivial properties and magnetism, realizing a spinChern insulator [2]. Besides the remarkable application for topological matter, artificial gauge fields, which rely on the coupling of spin states, offer also great insides into mutliorbital physics. In the second main research line reported in the thesis we study in collaboration with the experimental group of Leonardo Fallani, the controlled symmetry breaking on a 173Yb manybody system, where coupling between spin states is exploited to simulate the mechanism relevant for the physics of multiorbital materials, such as ironbased superconductors. In order to reveal this mechanism in cold atoms we focus on interacting SU(3) lattice fermions where the SU(3) spin symmetry is explicitly broken by a Raman coupling between the spin states. Combining experiments and theory, we demonstrate that this setup reveals orbitalselective physics and it shows that the SU(3)symmetrybreaking Raman coupling favours Mott localization and selective properties [3]. Our results show a clear evidence of orbitalselective correlations, which reflect in contrasting transport properties in different orbitals, the extreme case being an orbitalselective Mott state where only some of the orbitals are Mott localized while others remain metallic. Moreover, the coupling between spin states favors Mott localization with respect to the symmetric case, hence it reduces the critical interaction needed for a full Mott localization.
Mott transitions, topology, and magnetism of interacting fermions in confined geometries / Baumann, Karla Jana.  (2020 Aug 28).
Mott transitions, topology, and magnetism of interacting fermions in confined geometries.
Baumann, Karla Jana
20200828
Abstract
This thesis reports original research on strongly interacting fermions described by Hubbardlike models which can be realized with ultracold atom experiments. In particular, two main directions have been pursued: (i) the control of magnetic and topological properties in a honeycomb lattice through a suitable tuning of the trapping potential, and (ii) the possibility to observe orbitalselective Mott physics in a multicomponent Fermi system where the SU(N) symmetry is broken in a controlled way. The first line of research is based on the idea that increasing the strength of a trapping potential, one can trap a strongly interacting fermions in a limited portion of space, thereby changing their average density and the related magnetic properties. In particular it was demonstrated that this confinement protocol can be used to designeffective “nanoflakes” which are reminiscent of a solidstate proposal [1]. The second step was to extend the same philosophy to the socalled KaneMele model, a spinful version of the paradigmatic model proposed by Haldane which presents quantum Hall states. This model can be realized with coldatom systems using artificial gauge fields. In this thesis we consider a KaneMeleHubbard model where the electronic structure of the KaneMele model is supplemented by the onsite Hubbard interaction, allowing us to study the interplay between the correlations and magnetism induced by the repulsion, with the nontrivial topological properties. Also for this model, we follow the strategy discussed above, namely the possibility to engineer an effective “nanoflake” by tuning the lattice potential. The final outcome in this case is even reacher, because it leads, among other results, to a situation where the effective flake hosts an inhomogeneous state which presents at the same time topologically nontrivial properties and magnetism, realizing a spinChern insulator [2]. Besides the remarkable application for topological matter, artificial gauge fields, which rely on the coupling of spin states, offer also great insides into mutliorbital physics. In the second main research line reported in the thesis we study in collaboration with the experimental group of Leonardo Fallani, the controlled symmetry breaking on a 173Yb manybody system, where coupling between spin states is exploited to simulate the mechanism relevant for the physics of multiorbital materials, such as ironbased superconductors. In order to reveal this mechanism in cold atoms we focus on interacting SU(3) lattice fermions where the SU(3) spin symmetry is explicitly broken by a Raman coupling between the spin states. Combining experiments and theory, we demonstrate that this setup reveals orbitalselective physics and it shows that the SU(3)symmetrybreaking Raman coupling favours Mott localization and selective properties [3]. Our results show a clear evidence of orbitalselective correlations, which reflect in contrasting transport properties in different orbitals, the extreme case being an orbitalselective Mott state where only some of the orbitals are Mott localized while others remain metallic. Moreover, the coupling between spin states favors Mott localization with respect to the symmetric case, hence it reduces the critical interaction needed for a full Mott localization.File  Dimensione  Formato  

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