Electron-Hole Overlap Dictates the Hole Spin Relaxation Rate in Nanocrystal Heterostructures

Hole spin relaxation dynamics in CdTe/CdSe core-shell nanocrystals are measured by an ultrafast polarization transient grating technique. Photoexcited charge separation in type II structures suppresses the electron-hole exchange interaction and the hole spin relaxation time constant is found to increase from similar to 0.3 ps to similar to 10 ps at 293 K as the CdSe shell thickness increases from similar to 0.2 nm to similar to 2.4 nm. Analysis of these data suggests that spin relaxation in semiconductor nanostructures is tunable between type I and type II localization according to an electron-hole overlap function.