Seminar "Multiboson theory for the magnetoelectric helimagnet Cu2OSeO3" by Judit Romhanyi

 

Cu2OSeO3 is a magnetoelectric insulator exhibiting topologically nontrivial skyrmion-lattice phase. In Cu2OSeO3 the magnetic Cu2+ ions form a distorted pyrochlore lattice of corner sharing tetrahedra.

Recent ab initio density functional calculations show that there are two well separated exchange energy scales, dividing the system into strong and weak tetrahedra. Building on this fact, we perform a microscopic multi-boson theory which treats the strong tetrahedra fully quantum mechanically, and the weak couplings between them on a mean field level.

This theory captures the experimentally observed spin reduction and provides the excitation spectrum as well as the dynamical structure factors, pertinent to inelastic neutron scattering, Raman, and other spectroscopic probes. We also discuss magnetoelectric effect based on this theory and compare our results with ESR and neutron experiments.