Evidence of magnon generation in the fractional quantum Hall effect*

Magnons, low energy spin excitations in magnetic systems, have been recently observed in the integer quantum Hall effect in graphene, where magnons were generated and detected by non-equilibrium populations of integer edge channels. In this work, we study spin relaxation at a filling factor 2/3, where the transition between polarized (p) and unpolarized (u) states can be controlled by electrostatic gates. When current is injected from p to u region or vice versa, angular momentum conservation is satisfied by polarizing a nuclear bath via hyperfine interaction. Nuclear bath polarization can be measured independently in u and p regions via an Overhauser shift of the ferromagnetic transition. We found that for spin-lowering injection nuclei in both u and p regions are polarized, indicating omnidirectional spin diffusion, while for the spin-raising injection only nuclei in the p region are polarized. We attributed this asymmetry to the preferred generation of magnons in the p ferromagnetic region which efficiently carries angular momentum away from the u-p boundary.