Physics

Dr. Ranjani Sheshadri
IISc Bangalore

In this talk, I will focus on topological aspects and edge states of a spin system on a Kagome lattice. The model considered here is that of spins arranged on a Kagome lattice with the anisotropic XXZ interaction and the Dzyaloshinskii-Moriya interaction (DMI). I will begin with the rich phase diagram in the classical limit arising as a result of the interplay of the two interaction strengths. This will be followed by a spin-wave analysis in some of these phases. These spin-waves (or magnons) are studied using the Holstein-Primakoff transformations.   In the ferromagnetic phase in which all the spins point along the +z or -z direction the bulk bands are separated from each other by finite energy gaps. Finding the Chern numbers here one finds that, there are four topologically distinct phases sharing the same ground state spin-configuration.  Hence an infinite strip of the system hosts robust edge states which are directly related to the Chern number of the bands. The other phases also are found to have edge modes. However, these are not topologically protected because of the gapless nature of the energy dispersion.