DataSet_Hallmarks of ballistic terahertz magnon currents in an antiferromagnetic insulator

we here use femtosecond laser pulses to trigger ultrafast spin currents across thin films of the model antiferromagnet NiO in Py|NiO|Pt stacks, where permalloy (Py) and Pt serve as spin-current source and detector, respectively. We find that the spin-current pulses traversing NiO reach a velocity up toand experience increasing attenuation, delay and broadening as the NiO thickness is increased. We can consistently explain our observations by ballistic transport of incoherent magnons. The relaxation length ofisorder of magnitude larger than for ballistic conduction-electron spin transport in metals and, thus, relevant for potential applications. Methodologically, our all-optical and contact-free spin-conductance approach has large potential to characterize terahertz magnon transport in insulators with any kind of magnetic order.