Effects of a longitudinal magnetic field on spin injection and detection in InAs/GaAs quantum dot structures

Abstract

Abstract. Effects of a longitudinal magnetic field on optical spin injection and detection in InAs/GaAs quantum dot (QD) structures are investigated by optical orientation spectroscopy. An increase in optical and spin polarization of the QDs is observed with increasing magnetic field in the range of 0-2 T, and is attributed to suppression of exciton spin depolarization within the QDs that is promoted by hyperfine interaction and anisotropic electron-hole exchange interaction. This leads to a corresponding enhancement in spin detection efficiency of the QDs by a factor of up to 2.5. At higher magnetic fields when these spin depolarization processes are quenched, electron spin polarization in anisotropic QD structures (such as double QDs that are preferably aligned along a specific crystallographic axis) still exhibits rather strong field dependence under non-resonant excitation. In contrast, such field dependence is practically absent in more "isotropic" QD structures (e.g. single QDs). We attribute the observed effect to stronger electron spin relaxation in the spin injectors (i.e. wetting layer and GaAs barriers) of the lower-symmetry QD structures, which also explains the lower spin injection efficiency observed in these structures.PACS numbers: 73.21. La, 78.67.Hc, 72.25.Fe, 72.25.Rb IntroductionSemiconductor quantum dot (QD) structures are currently under intense investigations in view of their potential applications in spin-based quantum information technology and nanospintronics, as the three-dimensional carrier confinement in these structures promises suppression of many spin relaxation mechanisms that are predominant in semiconductors of higher dimensionality [1]. In threeand two-dimensional structures, the most important spin relaxation mechanisms such as the D'yakonov-Perel and Elliott-Yafet mechanisms are promoted by the motion of carriers. For confined carriers in QDs, the lack of carrier motion efficiently deactivates these spin relaxation mechanisms. Furthermore, their atomic-like, discrete energy level structure restricts efficiency of phonon-induced inelastic scattering processes. Hyperfine interactions of confined carriers with nuclear spins of host lattice atoms within QDs [2,3] and carrier-carrier exchange interaction [4] become the dominant spin relaxation mechanisms at low temperatures. The expected extended carrier spin lifetimes have been confirmed experimentally [5][6][7][8], and efficient room-temperature spin detection has also recently been demonstrated [9], which is encouraging for proposals of QDs in applications of quantum computing

Oblique Nuclear Quadrupole Interaction in Self-Assembled Structures Based on Semiconductor Quantum Dots

“…However, we should point out that X 0 , usually reported to have a spin lifetime less than 100 ps, should give rise to a broad background in the Hanle spectra [28] that has a negligible effect on the Hanle effect in the low-field regime (with a transverse magnetic field |B ⊥ | < 100 G) focused in this work. In the Faraday geometry, the longitudinal magnetic field B recovers the spin states of X 0 and produces a slow-varying monotonic increase of P PL as a function of |B | [29], which neither affects the results to be presented below. Figure 2(a) shows representative Hanle curves obtained from the QR sample in an external transverse magnetic field B ⊥ .…”

Coherent control with optical pulses for deterministic spin-photon entanglement

“…[1][2][3] Recent experiments, since 2010, have demonstrated optical control of exciton 4 and biexciton 5 generation, as well as control of the spin state of electrons, [6][7][8] holes, 9,10 and excitons [11][12][13][14] in single InAs quantum dots. Efforts continue to better characterize semiconductor quantum dots, including improved understanding of the effects of electric 15,16 and magnetic 17 fields, further studies of the energy levels, 18,19 room-temperature studies, 20 and many other critical measurements. [21][22][23][24][25][26] Several groups demonstrated new spin readout methods, [27][28][29] addressing one of DiVincenzo's criteria for quantum computing.…”

Increase in the efficiency of spin detection based on GaAsSb by applying a longitudinal magnetic field or a postgrowth annealing process

“…Under linearly polarized excitation, the spin imbalance is caused by spin relaxation from the upper branch spin state to the lower branch spin state introduced by Zeeman splitting. 15,16) The spin polarization degree P l as a function of B z can be calculated simply for a two-level spin system as 17,18)…”