Magnons and excitation continuum in XXZ triangular antiferromagnetic model: Application to $Ba_3CoSb_2O_9$

GHIOLDI, ESTEBAN A.; MEZIO, ALEJANDRO; MANUEL, LUIS O.; SINGH, RAJIV R. P.; OITMAA, JAN; TRUMPER, ADOLFO E.

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Lugar: New York; Año: 2015 vol. 91 p. 134423 - 134423

1098-0121

We investigate the excitation spectrum of the triangular-lattice antiferromagnetic XXZ model using series expansion and mean field Schwinger boson approaches. The single-magnon spectrum computed with series expansion exhibits rotonic minima at the middle points of the edges of the Brillouin zone, for all values of the anisotropy parameter in the range $0 leq J/J_z le1 1$. Based on the good agreement with series expansion for the single-magnon spectrum, we compute the full dynamical magnetic structure factor within the mean fieldSchwinger boson approach to investigate the relevance of the XXZ model for the description of the unusual spectrum found recently in Ba$_3$CoSb$_2$O$_9$. In particular, we obtain an extended continuum above the spin wave excitations, which is further enhanced and brought closer to those observed in Ba$_3$CoSb$_2$O$_9$ with the addition of a second neighbor exchange interaction approximately 15% of the nearest-neighbor value. Our results support the idea that excitation continuum with substantial spectral-weight are generically present in two-dimensional frustrated spin systems and fractionalization in terms of bosonic spinons presents an efficient way to describe them.