2014/07/21 by Ahmad K. Fumani, Fumani, A. Khastehdel, Jesse Berezovsky +1
Materials Science · Physics and Astronomy · #FOS: Physical sciences #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #Quantum Dots Synthesis And Properties #Quantum and electron transport phenomena #Semiconductor Quantum Structures and Devices
paper · pdf · doi:10.48550/arxiv.1407.5543
openalex publication_date 2014/07/21 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
To understand and optimize optical spin initialization in room temperature CdSe nanocrystal quantum dots (NCQDs) we studied the dependence of the time-resolved Faraday rotation signal on pump energy Ep in a series of NCQD samples with different sizes. In larger NCQDs, we observe two peaks in the spin signal vs. Ep, whereas in smaller NQCDs, only a single peak is observed before the signal falls to a low, broad plateau at higher energies. We calculate the spin-dependent oscillator strengths of optical transitions using a simple effective mass model to understand these results. The observed Ep dependence of the spin pumping efficiency (SPE) arises from the competition between the heavy hole (hh), light hole (lh) and split-off (so) band contributions to transitions to the conduction band. The two latter contributions lead to an electron spin polarization in the opposite direction from the former. At lower Ep the transitions are dominated by the hh band, giving rise to the low energy peaks. At higher Ep, the increasing contributions from the lh and so bands lead to a reduction in SPE. The different number of peaks in larger and smaller NCQDs is attributed to size-dependence of the ordering of the valence band states.