Ballistic propagation of large wave vector magnons in magnetically ordered materials (invited)

We present evidence of ballistic transport of energy by high-energy, large wave vector magnons in the antiferromagnet MnF2. Nonequilibrium magnons are created by heat pulses or by selective laser excitation throughout the Brillouin zone, using the magnon sideband or far-infrared (FIR) two-magnon absorptions. The ballistic magnon signal is extracted from the total observed signal and used to calculate the magnon velocity as a function of magnon energy. The results compare favorably with theory. Implications of our results to various types of magnetically ordered lattices are discussed.