Antiferromagnetic coupling between semiconductor quantum dots

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

doi:10.1016/s0921-4526(01)01394-1

Cited by 9 publications

(6 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…2, the behavior of the PL peak intensity the presence of an applied magnetic field in the non-DMS DLQD spectrum is now significantly different: the change of the PL intensity emitted by the CdSe QDs is much stronger than in the emission from the CdZnSe dots. A similar behavior has also been observed by others in DLQD structures involving III-V materials (specifically, in double layers involving InAs and InAlAs QDs [11]), suggesting that the PL intensity behavior observed in our DLQD is indeed characteristic of coupled QD structures.…”

Section: Non-dms Dms Cb Vbsupporting

confidence: 90%

Coupled II–VI semiconductor quantum dots: manipulation of spin polarization by inter‐dot exchange interaction

Lee

Furdyna

Dobrowolska

2005

phys. stat. sol. (c)

View full text Add to dashboard Cite

We have studied self-assembled QDs in the form of single-and double-QD layer systems. The double layers were formed either from CdSe and CdZnSe layers, or from CdSe and CdZnMnSe layers, separated by ZnSe barriers. When a magnetic field is applied to the CdSe/CdZnSe double-QD layer, the intensities of the circularly polarized PL peaks corresponding to the CdSe and CdZnSe layers exhibit significant differences, reflecting correspondingly large differences in the degrees of spin polarization of the CdSe and the CdZnSe QDs. This contrasts with the PL observed on single-layer CdSe or CdZnSe QD reference structures, both of which show nearly identical dependences on the field. The behavior observed on the double-layer QD structures is interpreted in terms of anti-parallel spin interaction between carriers localized in the coupled QD pairs. Such spin interaction is even more pronounced in double-layer structures in which CdZnMnSe QW or QDs are used instead of CdZnSe QDs, reflecting the high potential of magnetic quantum structures in the context of spin-polarized applications. IntroductionSpin states in quantum dots (QDs) have recently been proposed as viable candidates for quantum bits in quantum computing.[1] As an important step toward this application one must have a good understanding of spin phenomena in QDs, as well as the ability to control and manipulate spins localized in this way. Coupled QD pairs are especially interesting in this context, since they constitute the simplest and at the same time the most informative QD system for studying spin interactions in a highly-localized geometry. Theoretical calculations [2] predict that when QDs are coupled, spins localized in one QD tend to align anti-parallel (antiferromagnetically) with those in is neighbor. This automatically provides a handle for manipulating spin states in the QD geometry.

show abstract

Section: Non-dms Dms Cb Vbsupporting

confidence: 90%

Coupled II–VI semiconductor quantum dots: manipulation of spin polarization by inter‐dot exchange interaction

Lee

Furdyna

Dobrowolska

2005

phys. stat. sol. (c)

View full text Add to dashboard Cite

show abstract

“…4b, was evaluated to be 0.8 ns. In the conventional SK dots with large inhomogeneous broadening, greater spin polarization is observed at the high-energy side of the PL peak than at the low-energy side [3]. In the high-uniform QDs, the spin polarization at the high-energy side of the PL peak is equal to that at the low-energy side as shown in Fig.…”

mentioning

confidence: 85%

“…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].…”

mentioning

confidence: 99%

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

Murayama

Ohtsubo

Kitamura

et al. 2003

phys. stat. sol. (c)

Self Cite

View full text Add to dashboard Cite

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-

show abstract

“…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%

“…As a result, interesting phenomena such as an antiferromagnetic coupling of exciton spins have been reported. 10,14 The electronic states of each self-assembled dot correlate through tunneling and energytransfer processes even in a single-layer structure, if the sheet density of the dot is high, leading to close dot separations. 15,16 The high-density QD system holds great potential for device applications, because of their high intensities of optical signals, such as photoluminescence ͑PL͒, electroluminescence, and lasing.…”

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

View full text Add to dashboard Cite

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.

show abstract

Antiferromagnetic coupling between semiconductor quantum dots

Cited by 9 publications

References 12 publications

Coupled II–VI semiconductor quantum dots: manipulation of spin polarization by inter‐dot exchange interaction

Coupled II–VI semiconductor quantum dots: manipulation of spin polarization by inter‐dot exchange interaction

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

Contact Info

Product

Resources

About