Ultrafast dynamics in the Lifshitz-type 5d pyrochlore antiferromagnet Cd2Os2O7

We investigate the ultrafast dynamics of ${\mathrm{Cd}}₂{\mathrm{Os}}₂{\mathrm{O}}₇$, a prototype material showing a Lifshitz-type transition as a function of temperature. In the paramagnetic metallic state, the photoreflectivity shows a subpicosecond relaxation, followed by a featureless small offset. In the antiferromagnetic state slightly below ${T}_N$, however, the photoreflectivity resurges over hundreds of picoseconds, which goes beyond the usual realm of the effective-temperature model. Our observations are consistent with the Lifshitz phase transition of ${\mathrm{Cd}}₂{\mathrm{Os}}₂{\mathrm{O}}₇$ driven by the evolution of the local magnetic moment.