Full text
| |
| Author(s): |
Pedro Monteiro Cônsoli
Total Authors: 1
|
| Document type: | Master's Dissertation |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT) |
| Defense date: | 2020-09-22 |
| Examining board members: |
Eric de Castro e Andrade;
Thereza Cristina de Lacerda Paiva;
Rodrigo Gonçalves Pereira
|
| Advisor: | Eric de Castro e Andrade |
| Abstract | |
Over the past years, the physics of Kitaev\'s spin-1/2 honeycomb model and its extensions have attracted enormous interest, fueled by a pursuit of the fundamental understanding as well as experimental realizations of quantum spin-liquid phases. A notorious achievement in this field has been the discovery that, when applied in specific directions, a magnetic field can induce a gapped topological spin liquid in the Kitaev quantum magnet ∝-RuCl3. In parallel, the search for other magnets with strong spin-orbit coupling has resulted in recent proposals of material candidates to host spin-1 and spin-3/2 analogs of the Kitaev interaction. Remarkably, all of these materials display nontrivial responses to magnetic fields, such as strongly anisotropic magnetization processes and novel field-induced states, due to the lack of spin-rotational symmetry. Given such a rich background, this dissertation aims at expanding the current knowledge of the effects of magnetic fields on extended Kitaev systems with three different contributions. First, we employ a combination of linear and nonlinear spin-wave theory to study the ordered field-induced phases of the nearestneighbor Heisenberg-Kitaev model, which is often regarded as a minimal model to describe Kitaev magnetism for different spin quantum numbers S. By developing a consistent 1/S expansion, we analyze the influence of the leading-order quantum fluctuations on physical observables and phase diagrams of the experimentally relevant cases of S = 1/2, 1 and 3/2. Second, we consider a more realistic spin model to describe the low-temperature elastic response of ∝-RuCl3 in an applied magnetic field and small uniaxial pressure. Our results suggest that anomalous features found in experiments are indicative of an intermediate-field quantum paramagnetic regime. Finally, we return to the Heisenberg-Kitaev model in a magnetic field, but by now applying the numerical technique of exact diagonalization for S = 1/2. Besides finding good agreement with our spin-wave calculations, we report possible evidence for a new quantum tricritical point. (AU) | |
| FAPESP's process: | 17/22133-3 - Melting the vortex crystal in the Heisenberg-Kitaev model in a magnetic field |
| Grantee: | Pedro Monteiro Cônsoli |
| Support Opportunities: | Scholarships in Brazil - Master |