The search for experimentally tangible scenarios of spin liquids as topologically ordered quantum states of matter is one of the most vibrant subfields of contemporary condensed matter research. Honeycomb iridates and related materials have originally been suggested as possible candidates for hosting a spin-liquid state. Intriguingly, no quantum paramagnetic ground state has been discovered so far in these materials, posing fundamental challenges to determining an accurate underlying microscopic spin model. In our study we show that the second-neighbor Kitaev coupling is an important ingredient to such a microscopic description for the strong spin-orbit transition-metal oxide Na2IrO3.
We analyze the K1-K2 model from a variety of methodological perspectives. As a coherent picture emerges from the investigation, the K1-K2 model allows us to explain the onset of zigzag magnetic order that is also found experimentally. Furthermore, we find that the K1-K2 model is a suitable minimal description for resolving the substantially different nature of quantum and thermal fluctuations originating from such Kitaev couplings.