Events

Abstract: Recent experimental studies have raised an extensive interest on the excitation spectrum of spin-1/2 triangular magnets with XXZ magnetic anisotropy. Among the materials which were recently investigated, the cobaltite K2Co(SeO3)2 was shown to provide a realization of the XXZ model with an extremely strong degree of easy-axis anisotropy, close to the limit of an Ising model. Motivated by the inelastic neutron scattering studies on this compound, this presentation will report on a theoretical analysis of the excitation spectrum in the “up-up-down” and in the low-field phase of the model, focusing on the Ising limit in which the longitudinal exchange Jzz is much larger than the transverse exchange Jxy. In the “up-up-down” phase, stabilized by a c-axis oriented field, we study the magnon excitations, both in the framework of spin wave theory and within a perturbative expansion in the anisotropy parameter α = Jxy/Jzz ≪ 1. We show that the linear-spin wave (LSW) approximation, although exact at leading order in α, strongly misses the coefficients of the higher-order corrections in α. We argue that this discrepancy explains the deviations between LSW and scattering data observed in the up-up-down phase. The presentation will then discuss the spectrum in the low-field phase of the model, characterized by “spin-supersolid” order. We analyze in particular the first order of the non-linear spin wave theory (NLSWT), and discuss the complexity of this expansion in the strong coupling region relevant in K2Co(SeO3)2.