Negative circular polarization as a universal property of quantum dots

Taylor, Matthew; Spencer, Peter; Murray, R.

doi:10.1063/1.4916370

Cited by 11 publications

(10 citation statements)

References 18 publications

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“…Such negative CPD properties of QD-PL were previously explained by a spin flip-flop transition through scattering at QD-ES1 based on the formation of a negatively charged exciton with excess electrons in the QDs. [17][18][19][20][21][22][23][24][25] In this study, the transfer of electrons should be faster than that of holes owing to the faster tunneling rate within the SL. Therefore, excess electrons in the QDs can occur as with ndoped QDs.…”

mentioning

confidence: 97%

“…Such excess electrons in the QDs induce a luminescence counter-polarized to the initial excitation owing to the electron-hole spin flip-flop interactions. [17][18][19][20][21][22][23][24][25] Although the optical spin properties in QDs with excess electrons have been studied using n-doped QDs [17][18][19][20][21][22] or by means of an applied electric bias used to control the charge state of the QDs, [23][24][25] these properties have not been sufficiently explored in hybrid nanosystems. This understanding has significant implications for manipulating the optical spin properties of QD-based nanosystems.…”

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confidence: 99%

“…Therefore, excess electrons in the QDs can occur as with ndoped QDs. [17][18][19][20][21][22] To reveal the excitation power dependence of PL-CPD properties, we performed a time-resolved analysis of PL and its CPD of QD-ES1. Figure 2(a) shows the circularly polarized PL time profiles and corresponding CPD measured at 0.1, 1.5, and 7.5 mW.…”

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confidence: 99%

“…Here, we assume the spin injection from the SL to the QD-ES1, where a spin flip-flop transition through scattering can occur. [17][18][19][20][21][22][23][24][25] The rate equations can be written as follows:…”

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confidence: 99%

“…17,23,24 Here, the spin-flip time between the spin-split QD states may be different because the spin flip-flop interactions are linked to the occupation of QD-ES1. 22 Simulations of the transient CPD behavior as a function of time by varying s s1 are shown in Fig. 2(c).…”

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confidence: 99%

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Asymmetric spin relaxation induced by residual electron spin in semiconductor quantum-dot-superlattice hybrid nanosystem

Hiura

Hatakeyama

Takayama

et al. 2020

Applied Physics Letters

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Asymmetric spin relaxation induced by the residual electron spin in semiconductor quantum dots (QDs) adjacent to a superlattice (SL) was studied using spin-and time-resolved photoluminescence under the selective photoexcitation of the SL miniband states. Spin-polarized electrons were photoexcited in the SL barrier and then injected into the QDs through spin-conserving tunneling. The spin-polarized electron transport and the faster transport of the electrons as compared to the holes generate the residual majority electron spins in the QDs. A reversal of the optical spin polarity was observed at the ground state of the QDs, depending on the excitation powers. A rate equation analysis considering the individual spin-flip times between spin-split QD states indicates that the polarity reversal originates from the asymmetric spin-flip process at the excited state of the QDs. The asymmetric spin relaxation is associated with the selective relaxation of the spin-flipped electron and hole to the unoccupied ground state, which is induced by the existence of the residual majority electron spin at this state. In addition, we observed a clear recovery of the optical spin polarity by eliminating the existence of the residual electron spin through heavy p-doping. These findings are important to attain a fundamental understanding of the spin relaxation mechanism within the QDs and provide an insight into the manipulation of the optical spin polarity by controlling the residual electron spins in the QDs.

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confidence: 97%

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confidence: 99%

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confidence: 99%

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confidence: 99%

mentioning

confidence: 99%

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Asymmetric spin relaxation induced by residual electron spin in semiconductor quantum-dot-superlattice hybrid nanosystem

Hiura

Hatakeyama

Takayama

et al. 2020

Applied Physics Letters

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Electric-Field-Effect Spin Switching with an Enhanced Number of Highly Polarized Electron and Photon Spins Using p-Doped Semiconductor Quantum Dots

et al. 2021

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Electric-field-effect spin switching with an enhanced number of highly polarized electron and photon spins has been demonstrated using p-doped semiconductor quantum dots (QDs). Remote p-doping in InGaAs QDs tunnel-coupled with an InGaAs quantum well (QW) significantly increased the circularly polarized, thus electron-spin-polarized, photoluminescence intensity, depending on the electric-field-induced electron spin injection from the QW as a spin reservoir into the QDs. The spin polarity and polarization degree during this spin injection can be controlled by the direction and the strength of the electric field, where the spin direction can be reversed by excess electron spin injection into the QDs via spin scattering at the QD excited states. We found that the maximum degrees of both parallel and antiparallel spin polarization to the initial spin direction in the QW can be enhanced by p-doping. The doped holes without spin polarization can effectively contribute to this electric-field-effect spin switching after the initial electron spin injection selectively removes the parallel hole spins. The optimized p-doping induces fast spin reversals at the QD excited states with a moderate electric-field application, resulting in an efficient electric-field-driven antiparallel spin injection into the QD ground state. Further excess hole doping prevents this efficient spin reversal due to multiple electron−hole spin scattering, in addition to a spin-state filling effect at the QD excited states, during the spin injection from the QW into the QDs.

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Electric field control of spin polarity in spin injection into InGaAs quantum dots from a tunnel-coupled quantum well

Chen

Hiura

Takayama

et al. 2019

Applied Physics Letters

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Electric field control of spin polarity in spin injection into InGaAs quantum dots (QDs) from a tunnel-coupled quantum well (QW) was studied. The degree of freedom of the spin state in high-density QDs will play an important role in semiconductor spintronics such as a spin-functional optical device, where it is crucial to establish spin injection and manipulation by electric fields. To solve this subject in a layered device structure, electric field effects on spin injection from a 2-dimensional QW into 0-dimensional QDs were studied. Spin-polarized electrons were photo-excited in a QW and then injected into QDs via spin-conserving tunneling. After the injection, parallel spin states to the initial spin direction in the spin reservoir of QW were observed in QDs as a result of efficient spin injection, by circularly polarized photoluminescence indicating spin states in the QDs. Moreover, reversal of spin polarity was clearly observed at QD ground states, depending on the electric fields applied along the QD-QW growth direction. The tunneling rate of an electron is different from that of a hole and largely depends on the electric field, owing to electric field induced modifications of the coupled QD-QW potential. This results in negative trions in the QDs with anti-parallel spins to the initial ones in the QW, which is evidently supported by a significant effect of p-doping. The polarization degrees of both spin polarities can be optimized by excitation-spin density, in addition to the electric field strength.

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Negative circular polarization as a universal property of quantum dots

Cited by 11 publications

References 18 publications

Asymmetric spin relaxation induced by residual electron spin in semiconductor quantum-dot-superlattice hybrid nanosystem

Asymmetric spin relaxation induced by residual electron spin in semiconductor quantum-dot-superlattice hybrid nanosystem

Electric-Field-Effect Spin Switching with an Enhanced Number of Highly Polarized Electron and Photon Spins Using p-Doped Semiconductor Quantum Dots

Electric field control of spin polarity in spin injection into InGaAs quantum dots from a tunnel-coupled quantum well

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