Observation of interdot tunneling process of spin-polarized electrons

Tackeuchi, Atsushi; Nakata, Yoshihiro; Sasou, R.; Mase, K; Kuroda, Takeshi; Yokoyama, Naoki

doi:10.1016/s1386-9477(01)00048-0

Cited by 6 publications

(5 citation statements)

References 12 publications

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“…This lifetime is about twice as long as the radiative recombination time [6]. The same order of magnitude for the electron spin relaxation time was reported later for InAs quantum dots [7,8]. On the other hand, no spin decay has been observed on the exciton emission within a time interval of up to 20 ns in self-organized InAs/GaAs QDs by the time-resolved photoluminescence technique performed under strictly resonant excitation [9].…”

Section: Introductionsupporting

confidence: 78%

“…Although their size and density were different in different samples, the spin relaxation mechanisms intrinsic to QDs could hardly provide such a strong dependence of the spin lifetime on the Al content x in the barrier as we have observed in the experiment. It was observed recently that the spin relaxation time was not affected by a possible tunnelling process between dots [7]. Then, we remark that the measured Hanle curves are of Lorentzian shape and not Gaussian as it would be expected for the dominant mechanism of the electron spin dephasing via hyperfine interaction in QDs [11].…”

Section: Discussionsupporting

confidence: 53%

See 1 more Smart Citation

Spin lifetime from Hanle-effect measurements in samples with InAs quantum dots embedded in different Al_xGa_1−xAs matrices

Fürst

Pascher

Abalmassov

et al. 2005

Semicond. Sci. Technol.

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Excitation of electron hole pairs by circularly polarized light yields an electron spin polarization in InAs self-assembled quantum dots embedded in Al x Ga 1−x As. This spin polarization causes circular polarization of the photoluminescence light, its degree decreasing in a magnetic field perpendicular to the initial spin vector of the electrons (Hanle effect). With increasing aluminium content x the width of the Hanle curve is reduced from about 100 mT for x = 0 to 17.5 mT for x = 1. The corresponding electron spin lifetime increases with increasing x. For samples with QDs in the indirect gap matrix material AlAs, the spin lifetimes exceed 1.5 ns. A finite photoluminescence polarization evidences that the exciton spin lifetime inside a quantum dot cannot be much smaller than its recombination time. A single Lorentzian shape of the obtained Hanle curves and the observed field-independent part of the photoluminescence polarization could be explained by a small (zero) exciton g-factor in the dots at moderate magnetic fields, which could stem from the zero hole g-factor due to the electron-hole exchange interaction. The spin lifetime deduced from the Hanle curves could in this case be attributed to the thermalized electron capture time in the quantum dots.

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Section: Introductionsupporting

confidence: 78%

Section: Discussionsupporting

confidence: 53%

Spin lifetime from Hanle-effect measurements in samples with InAs quantum dots embedded in different Al_xGa_1−xAs matrices

Fürst

Pascher

Abalmassov

et al. 2005

Semicond. Sci. Technol.

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“…3b. The evaluated τ s1 is 1 ns, which is comparable to that of 1.3 ns in the conventional Stranski-Krastanov (SK) dots with large inhomogeneous broadening [2]. Using the PL results for the pumping power density of 200 W/cm 2 , which are regarded as a two-level system, the spin relaxation time in the second state, τ s2 , was derived from rate equations including the second state population of up-(down-) spin carriers, n 2+ (n 2-):…”

mentioning

confidence: 69%

“…For example, the spin in quantum dots (QDs) has a long relaxation time of approximately 1 ns [1,2]. Also, an antiferromagnetic order is found to be present between QDs by interdot exchange interaction [3].…”

mentioning

confidence: 99%

Observation of spin Pauli blocking in InAs high‐uniform quantum dots

Murayama

Ohtsubo

Kitamura

et al. 2003

phys. stat. sol. (c)

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We have investigated carrier spin dynamics in self-assembled InAs/GaAs high-uniform quantum dots. The high-uniform quantum dots allowed us to observe the spin dynamics in the ground state and that in the second state separately, without the disturbance of the inhomogeneous broadening. Spin Pauli blocking due to which the spin polarization in the second state is greater than that in the ground state has been clearly observed by time-resolved spin-dependent photoluminescence measurements. The spin relaxation times in the ground state and the second state were measured to be 1 ns and 0.8 ns, respectively.Recently, interesting features of electron spin have been revealed. For example, the spin in quantum dots (QDs) has a long relaxation time of approximately 1 ns [1,2]. Also, an antiferromagnetic order is found to be present between QDs by interdot exchange interaction [3]. Therefore, the quantum computation may be realized using carrier spins in QDs [4]. However, inhomogeneous broadening of QDs has made it difficult to understand spin-related phenomena because the ground-state energies of some QDs are equal to the second-state energies of the other QDs. To overcome this problem, we have adopted extremely high-uniform QDs as sample, which have the narrowest photoluminescence (PL) linewidth of 18.6 meV [5]. In this paper, we report the spin-dependent time-resolved PL measurements for InAs high-uniform QDs. We have clearly observed spin Pauli blocking due to which the spin polarization in the second state is greater than that in the ground state. Figure 1 shows the model of spin Pauli blocking schematically. An electron in the second state which has the same spin as that in the ground state cannot relax to the ground state due to the Pauli principle. This results in greater spin polarization in the second state. Let us consider a simple case that the total number N of electrons is photogenerated in the GaAs layer with the spin polarization, 2 /16N D dots on average will capture two down-spin electrons, and N 2 /16N D dots will capture two up-spin electrons. In the dots that have captured two electrons with the same spin (one in the ground state, and the other in the second state), the electron in the second state cannot relax to the ground state. The spin polarization in the se-

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“…In addition to this, correlations of the electronic spin states among dots are also found to be very attractive. [9][10][11][12][13] Spin dynamics in these coupled-QD systems with a diluted magnetic semiconductor ͑DMS͒ can be largely affected by the correlation of the wave functions of the spinpolarized carriers or excitons. As a result, interesting phenomena such as an antiferromagnetic coupling of exciton spins have been reported.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of exciton-spin injection, transfer, and relaxation in self-assembled quantum dots of CdSe coupled with a diluted magnetic semiconductor layer ofZn0.80Mn0.20Se

et al. 2007

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We study the dynamics of exciton-spin injection, transfer, and relaxation in self-assembled quantum dots ͑QDs͒ of CdSe coupled with a diluted magnetic semiconductor ͑DMS͒ layer of Zn 0.80 Mn 0.20 Se, where spinpolarized excitons can be injected from the DMS into the QDs. The degree of circular polarization P of excitonic photoluminescence ͑PL͒ at 5 T in the coupled QDs exhibits a rapid increase with increasing delay time, up to +0.3 at 25 ps after the pulse excitation of the DMS by a linearly polarized light. This development of a positive P value directly reflects the spin-injection dynamics from the DMS, since the intrinsic polarization of the QD excitons due to Zeeman splitting is P ϳ −0.1 when only the QDs are selectively excited. The P value gradually decays with time after reaching its maximum, as a result of the exciton-spin relaxation with a time constant of 800 ps in the QDs. Time-resolved circularly polarized PL spectra immediately after the pulse excitation directly show the exciton-energy dependence of the spin-injection dynamics in the QD ensemble, where two-dimensional-like QDs with higher exciton energies show higher receptivity to the spin-polarized excitons than three-dimensional-like dots with lower exciton energies. A rate equation analysis reveals all time constants responsible for the spin-injection dynamics. We deduce a time constant of 10 ps for the spin injection. The spin-injection efficiency of 0.94 is also obtained, which corresponds to the ratio between the number of the spin-polarized excitons responsible for the rise of the positive P value in the QD emission and the total number of the excitons injected from the DMS. Moreover, we observe that interdot exciton transfer significantly affects the P value within the QD emission band after the fast spin injection, in addition to the spin relaxation within the QDs.

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Observation of interdot tunneling process of spin-polarized electrons

Cited by 6 publications

References 12 publications

Spin lifetime from Hanle-effect measurements in samples with InAs quantum dots embedded in different Al_xGa_1−xAs matrices

Spin lifetime from Hanle-effect measurements in samples with InAs quantum dots embedded in different Al_xGa_1−xAs matrices

Observation of spin Pauli blocking in InAs high‐uniform quantum dots

Dynamics of exciton-spin injection, transfer, and relaxation in self-assembled quantum dots of CdSe coupled with a diluted magnetic semiconductor layer ofZn0.80Mn0.20Se

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Observation of interdot tunneling process of spin-polarized electrons

Cited by 6 publications

References 12 publications

Spin lifetime from Hanle-effect measurements in samples with InAs quantum dots embedded in different AlxGa1−xAs matrices

Spin lifetime from Hanle-effect measurements in samples with InAs quantum dots embedded in different AlxGa1−xAs matrices

Observation of spin Pauli blocking in InAs high‐uniform quantum dots

Dynamics of exciton-spin injection, transfer, and relaxation in self-assembled quantum dots of CdSe coupled with a diluted magnetic semiconductor layer ofZn0.80Mn0.20Se

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Spin lifetime from Hanle-effect measurements in samples with InAs quantum dots embedded in different Al_xGa_1−xAs matrices

Spin lifetime from Hanle-effect measurements in samples with InAs quantum dots embedded in different Al_xGa_1−xAs matrices