Coupled dynamics of long-range and cluster-internal spin order in the cluster Mott insulator Cu2OSeO3

Cu4 triplet clusters form the relevant spin entities for the formation of long-range magnetic order in the cluster Mott insulator Cu2OSeO3. Using time-resolved Raman spectroscopy, we probed photoinduced spin and lattice dynamics in this cluster magnet. Multiple picosecond-decade spin-lattice relaxation dynamics is observed, evidencing a separation of the order parameter dynamics into disordering of long-range and cluster-internal order on the tens and 100s on the picosecond timescale, respectively. We argue that this separation originates in vastly different interaction strengths between low- and high-energy spin cluster excitations and acoustic phonons. Our results exemplify the double-order parameter dynamics intrinsic to the novel quantum material class of cluster Mott insulators.