Melting the vortex crystal in the Heisenberg-Kitaev model in a magnetic field

Abstract

We will investigate in this project exotic phases of matter which emerge due tothe combination of strong spin-orbit coupling and electronic correlations, giving raisethe so-called spin-orbit Mott insulators. As systems of interest, we have in mindthe materials alpha-RuCl3 and A2IrO3 (A=Na, Li), which are well described by theHeisenberg-Kitaev model. In particular, we focus on the alpha-RuCl3, a compoundthat presents strong evidence of a spin liquid phase in the presence of an externalmagnetic field. We want to investigate how some of the unusual magnetic phasesencountered in the classical limit of the Heisenberg-Kitaev model, such as a vortexcrystal, are destroyed in the presence of quantum fluctuations. We will study thismodel using spin-wave theory and we want to consistently obtain the phase diagramup to order 1/S. Because the phases in the model are non-collinear, one has to takeinto account cubic terms in the magnon Hamiltonian for a consistent 1/S expansion,thus rendering the calculations rather challenging. (AU)