Using the trion as an optical probe, we uncover novel electron spin dynamics in $\mathrm{CdSe}/\mathrm{ZnSe}$ Stranski-Krastanov quantum dots. The longitudinal spin lifetime obeys an inverse power law associated with recharging processes in the dot ensemble. No hint at spin-orbit mediated spin relaxation is found. At very weak magnetic fields ($<50\mathrm{mT}$), electron spin dynamics related to the hyperfine interaction with the lattice nuclei is uncovered. A strong Knight field gives rise to nuclear ordering and formation of dynamical polarization on a $100\mathrm{\text{−}}\mu \mathrm{s}$ time scale under continuous electron spin pumping. The associated spin transients are temperature robust and can be observed up to 100 K.

• Received 27 February 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.056602