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.