Effect of μ4-O Sites on the Ultrafast Dynamics of Neutral Magnetic Copper Oxide Clusters

The ultrafast dynamics of sub-nanometer neutral copper oxide clusters are examined with pump probe spectroscopy. Upon absorp-tion of an ultraviolet (400 nm) photon, all clusters exhibit a sub-picosecond lifetime that we attribute to carrier relaxation. We cal-culate the ground state structures and spin configurations of the neutral clusters using density functional theory to identify struc-tural features that facilitate relaxation. By comparing results across 35 clusters, ranging between Cu3O3 and Cu16O8, we find evi-dence that strong ferromagnetic coupling influences the relaxation dynamics of copper oxide clusters. The total spin magnetic mo-ments increment with addition/subtraction of each Cu atoms away from the (Cu2O)n stoichiometry and reach as high as 5 μB in the larger clusters described. The excited state lifetimes increase almost linearly by ~40 fs per additional Cu atom on the sub-ps time-scale. In each series, the formation of μ4-O atoms associated with terminal Cu atoms consistently deviate from the trendline by increasing excited state relaxation rates.