Dynamical spectra of frustrated magnets
Understanding the nature of the excitation spectrum in frustrated magnets is of fundamental importance, in particular for the experimental detection of candidate materials for the realization of the spin liquid phase. However, current theoretical and numerical techniques have limited capabilities, especially in obtaining the dynamical structure factor, which gives a crucial characterization of the ultimate nature of the quantum state and may be directly assessed by inelastic neutron scattering experiments.
The work by Francesco Ferrari (SISSA) and Federico Becca (Università di Trieste) investigates the low-energy properties of the frustrated S=1/2 Heisenberg model on the triangular lattice, by a dynamical variational Monte Carlo approach that provides accurate results on spin models. The motivation of this work comes from several recent results of neutron scattering experiments on different magnetic compounds which display a triangular lattice structure (e.g. Ba3CoSb2O9, YbMgGaO4, NaYbO2).
In the unfrustrated phase of the model, the spectrum displays a well-defined magnon branch in the whole Brillouin zone, in contrast with the magnon decay predicted by spin wave analysis. In addition, a strong renormalization of the spin wave dispersion is observed, with the appearance of additional roton modes. On the other hand, in the frustrated regime of the model, originating from the competition of the superexchange couplings, a gapless spin liquid phase is stabilized, whose excitations suggest the importance of emergent gauge fields for the description of the low-energy physics of the system.
Dated: August 16, 2019