Seminarium Fizyki Materii Skondensowanej

I will discuss examples of one- and quasi-one-dimensional frustratedspin systems. Firstly, I will present results related to ageometrically frustrated chain, namely the ferromagnetic J1antiferromagnetic J2 chain. This system exhibits a Haldane gapsupported by a special AKLT-like valence bond solid state in aspecific region of the coupling ratio. Secondly, I will focus onexchange frustration and present results for the Kitaev-Heisenbergmodel on a chain and on a two-legged ladder. Remarkably, the phasediagram of the ladder is extremely similar to that of the honeycombmodel and the differences can be explained in terms of the differentdimensionalities. In particular, the ladder exhibits a topologicallynon-trivial phase with no long-range order, i.e., a spin liquid.