Spin polarization of the neutral exciton in a single InAs quantum dot at zero magnetic field

Abstract

A high degree of spin polarization for the neutral exciton in individual quantum dots, at zero external magnetic field, is monitored. While a high polarization degree is commonly observed for the charged exciton, a negligible polarization has been predicted for the neutral exciton. The exceptionally high polarization (andgt;60%) observed here is explained in terms of a dynamical nuclear polarization field, stabilizing the electron spin. Such polarization of the quantum dot nuclei, in case of the neutral exciton, is possible due to unequal capture time of electrons and holes.Original Publication:Evgenii Moskalenko, L A Larsson and Per-Olof Holtz, Spin polarization of the neutral exciton in a single InAs quantum dot at zero magnetic field, 2009, PHYSICAL REVIEW B, (80), 19, 193413.http://dx.doi.org/10.1103/PhysRevB.80.193413Copyright: American Physical Societyhttp://www.aps.org

Manipulating the spin polarization of excitons in a single quantum dot by optical means

“…9͒ but has been ascribed to the faster capture of electrons as compared to holes into the QD providing a time interval, when the QD is populated by a sole electron, which can then polarize the QD lattice nuclei. 11,12 In contrast to single laser excitation, which only results in X 0 , when adding a second infrared ͑IR͒ laser excitation X + is formed, as was demonstrated by us earlier. 13 An even higher polarization is measured for X + , c =73%, which is considered to be an upper bound for spin polarization of electrons captured into the QD from the wetting layer ͑WL͒.…”

“…10, the QD nuclei are polarized by an electron in the presence of two holes ͑i.e., during the radiative lifetime of X + ͒, while in the present case, the nuclei are polarized by a sole electron ͑i.e., without a hole͒ in the QD. 11 When a hole is subsequently captured into the QD, the electron has the possibility to recombine with it, resulting in the X 0 PL line. The larger magnitudes for the nuclear and electron polarizations could be understood in terms of a different QD composition in our case ͑nominally pure InAs͒ with respect to the case in Ref.…”

“…Detailed descriptions of the sample and of the experimental setup are given elsewhere. [11][12][13] c was determined as c = ͑I co − I cross ͒ / ͑I co + I cross ͒, where I co ͑I cross ͒ corresponds to the spectrally integrated PL signal of the co͑cross-͒circular components.…”

Circularly polarized emission from ensembles of InAs/GaAs quantum dots

“…Indeed, in our previous study on the charging of single QDs with extra electrons by pure optical means performed on another part of the same sample, the concentration of residual impurities in our nonintentionally-doped sample was estimated to be % 10 13 cm À3 . 18 This shows that the total number of extra (noncompensated) carriers which could be created by the laser within the excited volume [% 6.3 Â 10 À13 cm 3 (Ref.…”

“…6,7 However, a relatively high q c was also recently observed for the neutral exciton in individual InAs QDs at B ext ¼ 0. 12,13 This effect was explained in terms of the generation of a nuclear field (B N ) which effectively suppresses x ex , thus playing the role of B ext to "stabilize" the electron spin. It has been demonstrated 14 that an efficient nuclear spin pumping could also be achieved for the neutral exciton exposed to an external magnetic field.…”