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Register a new userConfinement-enhanced spin relaxation for electron ensembles in large quantum dots
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We present a numerical study of spin relaxation in a semiclassical electron ensemble in a large ballistic quantum dot. The dot is defined in a GaAs/AlGaAs heterojunction system with a two-dimensional electron gas, and relaxation occurs due to Dresselhaus and Rashba spin orbit interaction. We find that confinement in a micronscale dot can result in strongly enhanced relaxation with respect to a free two-dimensional electron ensemble, contrary to the established result that strong confinement or frequent momentum scattering reduces relaxation. This effect occurs when the size of the system is on the order of the spin precession length, but smaller than the mean free path.
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We estimate the spin relaxation rate due to spin-orbit coupling and acoustic phonon scattering in weakly-confined quantum dots with up to five interacting electrons. The Full Configuration Interaction approach is used to account for the inter-electron repulsion, and Rashba and Dresselhaus spin-orbit couplings are exactly diagonalized. We show that electron-electron interaction strongly affects spin-orbit admixture in the sample. Consequently, relaxation rates strongly depend on the number of carriers confined in the dot. We identify the mechanisms which may lead to improved spin stability in few electron (>2) quantum dots as compared to the usual one and two electron devices. Finally, we discuss recent experiments on triplet-singlet transitions in GaAs dots subject to external magnetic fields. Our simulations are in good agreement with the experimental findings, and support the interpretation of the observed spin relaxation as being due to spin-orbit coupling assisted by acoustic phonon emission.
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We investigate phonon-induced spin and charge relaxation mediated by spin-orbit and hyperfine interactions for a single electron confined within a double quantum dot. A simple toy model incorporating both direct decay to the ground state of the double dot and indirect decay via an intermediate excited state yields an electron spin relaxation rate that varies non-monotonically with the detuning between the dots. We confirm this model with experiments performed on a GaAs double dot, demonstrating that the relaxation rate exhibits the expected detuning dependence and can be electrically tuned over several orders of magnitude. Our analysis suggests that spin-orbit mediated relaxation via phonons serves as the dominant mechanism through which the double-dot electron spin-flip rate varies with detuning.
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The spin relaxation time $T_{1}$ in zinc blende GaN quantum dot is investigated for different magnetic field, well width and quantum dot diameter. The spin relaxation caused by the two most important spin relaxation mechanisms in zinc blende semiconductor quantum dots, {i.e.} the electron-phonon scattering in conjunction with the Dresselhaus spin-orbit coupling and the second-order process of the hyperfine interaction combined with the electron-phonon scattering, are systematically studied. The relative importance of the two mechanisms are compared in detail under different conditions. It is found that due to the small spin orbit coupling in GaN, the spin relaxation caused by the second-order process of the hyperfine interaction combined with the electron-phonon scattering plays much more important role than it does in the quantum dot with narrower band gap and larger spin-orbit coupling, such as GaAs and InAs.
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