Spin relaxation mechanism of hopping transport in a 2D asymmetric quantum dot array
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Spin Relaxation Mechanism of Hopping Transport in a 2D Asymmetric Quantum Dot Array A. F. Zinov’eva*, A. V. Nenashev, and A. V. Dvurechenskiœ Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia *e-mail: [email protected] Received December 11, 2006
Abstract—Spin relaxation is studied in the hopping conduction mode in 2D arrays of quantum dots (QDs) with structural asymmetry. It is shown that the absence of the “up–down” symmetry in a QD leads to the emergence of a new spin relaxation mechanism in tunneling in a 2D QD array. The difference in spin relaxation mechanisms for symmetric and asymmetric QDs is demonstrated on the basis of theoretical analysis of an elementary event (jump between two tunnel-coupled dots). It is shown that spin flip during tunneling between QDs is the main spin relaxation mechanism in the transport in dense arrays of QDs in Ge placed in weak (1–10 T) magnetic fields. PACS numbers: 71.70.Ej, 72.25.Rb, 73.21.La DOI: 10.1134/S1063776107080110
1. INTRODUCTION The problem of spin information transmission and storage in semiconducting nanostructures remains urgent in connection with several projects for designing devices and logical circuits using the spin degree of freedom [1–4]. One of the objects attractive from this point of view is the spin of a carrier localized at a quantum dot (QD). Spin in a QD attracts the attention of researchers since, first, spin information can be preserved for a long time and, second, the spin of an individual charge carrier can be controlled quite easily. One of the methods for producing QDs is self-organization in the course of heteroepitaxy of materials with different lattice constants. This method can be used for obtaining QD arrays with a high density on the order of 1011–1012 cm–2 and a homogeneity of about 10–20% [5]. Research aimed at producing ordered QD arrays is being carried out, and certain advances have been made in this direction [6, 7]. Charge transport in dense QD arrays occurs in the hopping conduction mode. For this reason, analysis of spin relaxation in the course of spin conduction becomes important. Some authors [8, 9] carried out research for semiconductors without a symmetry center (e.g., GaAs). It was proposed that the D’yakonov–Perel mechanism plays a decisive role not only in spin relaxation of free electrons in the conduction band, but also for electrons localized at impurities and participating in hopping conduction. The D’yakonov–Perel mechanism is not operative in semiconducting systems with a center of inversion (such as Ge or Si). If, however, the system possesses structural asymmetry, spin relaxation mechanisms associated with spin–orbit interaction (e.g., for 2D systems) becomes active due to the Bychkov–Rashba interaction
[10]. It was shown in [11] that the spin of a charge carrier experiencing resonant tunneling between QDs with structural asymmetry rotates about the effective magnetic field whose direction depends on the direction of tunneling. This me
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