Long-lived electron spin coherence in CdSe/Zn(S,Se) self-assembled quantum dots

Abstract

The electron spin coherence in $n$-doped and undoped, self-assembled CdSe/Zn(S,Se) quantum dots has been studied by time-resolved pump-probe Kerr rotation. Long-lived spin coherence persisting up to 13 ns after spin orientation has been found in the $n$-doped quantum dots, outlasting significantly the lifetimes of charge neutral and negatively charged excitons of 350--530 ps. The electron spin dephasing time as long as 5.6 ns has been measured in a magnetic field of 0.25 T. Hyperfine interaction of resident electrons with nuclear spin fluctuations is suggested as the main limiting factor for the dephasing time. The efficiency of this mechanism in II-VI and III-V quantum dots is analyzed.