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Register a new userStationary and transient leakage current in the Pauli spin blockade
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We study the effects of cotunneling and a non-uniform Zeeman splitting on the stationary and transient leakage current through a double quantum dot in the Pauli spin blockade regime. We find that the stationary current due to cotunneling vanishes at low temperature and large applied magnetic field, allowing for the dynamical preparation of a pure spin ground state, even at large voltage bias. Additionally, we analyze current that flows between blocking events, characterized, in general, by a fractional effective charge $e^*$. This charge can be used as a sensitive probe of spin relaxation mechanisms and can be used to determine the visibility of Rabi oscillations.
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We present measurements on gate-defined double quantum dots in Ge-Si core-shell nanowires, which we tune to a regime with visible shell filling in both dots. We observe a Pauli spin blockade and can assign the measured leakage current at low magnetic fields to spin-flip cotunneling, for which we measure a strong anisotropy related to an anisotropic g-factor. At higher magnetic fields we see signatures for leakage current caused by spin-orbit coupling between (1,1)-singlet and (2,0)-triplet states. Taking into account these anisotropic spin-flip mechanisms, we can choose the magnetic field direction with the longest spin lifetime for improved spin-orbit qubits.
We investigate spin relaxation in a silicon double quantum dot via leakage current through Pauli blockade as a function of interdot detuning and magnetic field. A dip in leakage current as a function of magnetic field on a sim 40 mT field scale is attributed to spin-orbit mediated spin relaxation. On a larger (sim 400 mT) field scale, a peak in leakage current is seen in some, but not all, Pauli-blocked transitions, and is attributed to spin-flip cotunneling. Both dip and peak structure show good agreement between theory and experiment.
Pauli spin blockade (PSB) is a significant physical effect in double quantum dot (DQD) systems. In this paper, we start from the fundamental quantum model of the DQD with the electron-electron interaction being considered, and then systematically study the PSB effect in DQD by using a recently developed non-perturbative method, the hierarchical equations of motion (HEOM) approach. The physical picture of the PSB is elucidated explicitly and the gate voltage manipulation is described minutely, which are both qualitatively consistent with the experimental measurements. When dotdot exchange interaction is involved, the PSB effect may be lifted by the strong antiferromagnetic exchange coupling.
By means of time-resolved optical orientation under strong optical pumping, the k-dependence of the electron spin-flip time (t_sf) in undoped GaAs is experimentally determined. t_sf monotonically decreases by more than one order of magnitude when the electron kinetic energy varies from 2 to 30 meV. At the high excitation densities and low temperatures of the reported experiments the main spin-flip mechanism of the conduction band electrons is the Bir-Aronov-Pikus. By means of Monte-Carlo simulations we evidence that phase-space filling effects result in the blocking of the spin flip, yielding an increase of t_sf with excitation density. These effects obtain values of t_sf up to 30 ns at k=0, the longest reported spin-relaxation time in undoped GaAs in the absence of a magnetic field.
We detect in real time inter-dot tunneling events in a weakly coupled two electron double quantum dot in GaAs. At finite magnetic fields, we observe two characteristic tunneling times, T_d and T_b, belonging to, respectively, a direct and a blocked (spin-flip-assisted) tunneling. The latter corresponds to lifting of a Pauli spin blockade and the tunneling times ratio eta=T_b/T_d characterizes the blockade efficiency. We find pronounced changes in the behavior of eta upon increasing the magnetic field, with eta increasing, saturating and increasing again. We explain this behavior as due to the crossover of the dominant blockade lifting mechanism from the hyperfine to spin-orbit interactions and due to a change in the contribution of the charge decoherence.
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