Ghost modes and continuum scattering in the dimerized distorted kagome lattice antiferromagnet Rb${}_2$Cu${}_3$SnF${}_{12}$

Abstract

High intensity pulsed neutron scattering reveals a new set of magnetic excitations in the pinwheel valence bond solid state of the distorted kagome lattice antiferromagnet Rb${}_2$Cu${}_3$SnF${}_{12}$. The polarization of the dominant dispersive modes (2 meV $<\hslash \ddot{I}‰<$7 meV) is determined and found consistent with a dimer series expansion with strong Dzyaloshinskii-Moriya interactions ($D/J=0.18$). A weakly dispersive mode near 5 meV and shifted "ghosts" of the main modes are attributed to the enlarged unit cell below a $T=215$ K structural transition. Continuum scattering between 8 meV and 10 meV might be interpreted as a remnant of the kagome spinon continuum [T.-H. Han et al., Nature 492, 406 (2012)]

7 pages, 5 figures