Spin-orbit and electronic interactions in narrow-gap quantum dots

Destefani, C. F.; Ulloa, Sergio E.; Marques, G. E.

doi:10.1103/physrevb.70.205315

Cited by 44 publications

(30 citation statements)

References 39 publications

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“…Spin-orbit effects on single dots have been already extensively investigated. [27][28][29][30][31][32][33][34][35][36][37][38] In this paper we investigate the role of spin-orbit coupling, represented by the Dresselhaus ͑both linear and cubic͒ and Bychkov-Rashba terms, in spin and charge properties of two laterally coupled quantum dots based on GaAs materials parameters. We perform numerically exact calculations of the energy spectrum using the method of finite differences.…”

Section: Introductionmentioning

confidence: 99%

Spin-orbit effects in single-electron states in coupled quantum dots

2005

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Spin-orbit effects in single-electron states in laterally coupled quantum dots in the presence of a perpendicular magnetic field are studied by exact numerical diagonalization. Dresselhaus ͑linear and cubic͒ and Bychkov-Rashba spin-orbit couplings are included in a realistic model of confined dots based on GaAs. Group theoretical classification of quantum states with and without spin-orbit coupling is provided. Spin-orbit effects on the g factor are rather weak. It is shown that the frequency of coherent oscillations ͑tunneling amplitude͒ in coupled dots is largely unaffected by spin-orbit effects due to symmetry requirements. The leading contributions to the frequency involves the cubic term of the Dresselhaus coupling. Spin-orbit coupling in the presence of a magnetic field leads to a spin-dependent tunneling amplitude, and thus to the possibility of spin to charge conversion, namely, spatial separation of spin by coherent oscillations in a uniform magnetic field. It is also shown that spin hot spots exist in coupled GaAs dots already at moderate magnetic fields, and that spin hot spots at zero magnetic field are due to the cubic Dresselhaus term only.

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Section: Introductionmentioning

confidence: 99%

Spin-orbit effects in single-electron states in coupled quantum dots

2005

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“…Longer τ s is observed for the intra LL case than for the inter LL case in the whole ∆ ST region explored. This might reflect the different orbital quantum numbers involved in each case, which are relevant to the orbital effect on the phonon emission and spin-orbit interaction [13,14]. However, the precise mechanism is not clear yet.…”

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confidence: 99%

Electrical Pump-and-Probe Study of Spin Singlet-Triplet Relaxation in a Quantum Dot

et al. 2005

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Spin relaxation from a triplet excited state to a singlet ground state in a semiconductor quantum dot is studied by employing an electrical pump-and-probe method. Spin relaxation occurs via cotunneling when the tunneling rate is relatively large, confirmed by a characteristic square dependence of the relaxation rate on the tunneling rate. When cotunneling is suppressed by reducing the tunneling rate, the intrinsic spin relaxation is dominated by spin-orbit interaction. We discuss a selection rule of the spin-orbit interaction based on the observed double-exponential decay of the triplet state.Electron spin in semiconductors has been a focus of research in the context of spintronics, in which spin is manipulated with spin-orbit coupling [1,2], and of quantum computation, in which spin carries a quantum information [3]. In contrast to two-dimensional electron gas (2DEG) with continuum density of states, electron spin in a quantum dot (QD) is basically free from elastic scattering, and the resulting long-lived spin states are favorable for spin-based applications. Indeed, relaxation times of more than 100 µs have been reported in QDs between Zeeman sublevels [4,5,6], as well as between a spin triplet and a singlet state [7,8]. These relaxation processes have been discussed in terms of either spin-orbit interaction or the cotunneling effect. In this Letter, we study spin relaxation from a triplet state to a singlet state in a lateral QD, in which all the relevant parameters can be controlled with the gate voltages. We observe smooth transition of the relaxation mechanism from the cotunneling regime to the spin-orbit regime by changing tunneling rates. The decay of the excited triplet state follows a single exponential curve in most conditions, but double exponential behavior is observed at a particular magnetic field where the triplet state crosses another state. This might be related to the long-lived spin-entanglement state under strong spin-orbit interaction.Figure 1(a) shows a scanning electron micrograph (SEM) image of our QD device. The AlGaAs/GaAs 2DEG is constricted by combined dry-etching and surface Shottky gates. We use only the three gates on the right-hand side to form a single QD as shown by the white circle. All the measurements are performed in a dilution refrigerator at ∼90 mK with magnetic field, B, applied perpendicularly to the 2DEG.The dot used in this study has charging energy of U ∼ 2 meV and electron number N ∼ 8. When the magnetic field is not very small (B > 0.4 T), electron orbitals in a QD can be classified by Landau level (LL) index, to which they approach in the high field limit [9]. Many-body correction of direct and exchange Coulomb interactions induces spin and orbital transitions associated with different LLs in low magnetic field, but with the same LL in high magnetic field [10]. Figure 1(b) shows an observed DC current, I, through the dot as a func-

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“…For low energies, we may consider only the k- linear term in BIA term [3]. Effects associated to the kquadratic and k-cubic BIA terms are under investigation and will be discussed elsewhere.…”

Section: Theoretical Formulationmentioning

confidence: 99%