Exciton dynamics and phase memory in MnF2

The time taken for the lowest T14 excitons in MnF2 to scatter across the Brillouin zone, i.e., to lose all phase memory, has been measured using a technique of resonant optical pumping and monochromatic fluorescence detection. At 1.9 K these very narrow-band excitons retain some phase memory for up to 1 μsec. It is also found that excitons with rather well-defined momenta are created in the decay of exciton-magnon states, but not in the decay of exciton-phonon states. This determines probable decay mechanisms for these two-particle states. © 1973 The American Physical Society.