Thesis defense of Leanna Blanche Müller
- Defense
The inorganic compound BiCu2PO6 contains tubelike structures, which are described magnetically by weakly coupled frustrated spin ladders with a finite energy gap. The elementary excitations are triplons of which the degeneracy is lifted due to Dzyaloshinskii-Moriya interactions. In certain regions of the Brillouin zone the lifetime of the triplon excitation modes becomes finite due to the hybridization of the single-triplon with the two-triplon states. In addition, the dispersions of these triplon modes show a striking down-bending before ceasing to exist. In experiment, BiCu2PO6 shows various types of decay processes, which can be caused by different symmetry breaking interactions. In previous studies, we established a minimal model to include all symmetry-allowed interactions, such as the Dzyaloshinskii-Moriya interaction. Based on this minimal model, we show in this thesis that isotropic and anisotropic effects are responsible for noticeable quasiparticle decay and certain down-shifts of the single-triplon energies. The analyses are based on a deepCUT approach for the isotropic case augmented by a perturbative treatment of the anisotropic couplings inducing quasiparticle decay at zero temperature.