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Register a new userTime domain optical manipulation of exciton and nuclear spin in a single self-assembled quantum dot
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We have demonstrated experimentally the manipulation of exciton and nuclear spins in a single self-assembled In$_{0.75}$Al$_{0.25}$As/Al$_{0.3}$Ga$_{0.7}$As quantum dot. The oscillation of exciton and nuclear spin polarizations were clearly observed. The switching of the emissions in Zeeman split pair indicates that the exciton pair with opposite spins was created coherently via the continuum states and that we can control the electron and nuclear spin polarizations only by changing the delay time of the cross-linearly-polarized pulses. These suggest the high potentiality of electron and nuclear spin manipulation in a single QD via the continuum state.
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We have fabricated a lateral double barrier magnetic tunnel junction (MTJ) which consists of a single self-assembled InAs quantum dot (QD) with ferromagnetic Co leads. The MTJ shows clear hysteretic tunnel magnetoresistance (TMR) effect, which is evidence for spin transport through a single semiconductor QD. The TMR ratio and the curve shapes are varied by changing the gate voltage.
We present a theory and experiment demonstrating optical readout of charge and spin in a single InAs/GaAs self-assembled quantum dot. By applying a magnetic field we create the filling factor 2 quantum Hall singlet phase of the charged exciton. Increasing or decreasing the magnetic field leads to electronic spin-flip transitions and increasing spin polarization. The increasing total spin of electrons appears as a manifold of closely spaced emission lines, while spin flips appear as discontinuities of emission lines. The number of multiplets and discontinuities measures the number of carriers and their spin. We present a complete analysis of the emission spectrum of a single quantum dot with N=4 electrons and a single hole, calculated and measured in magnetic fields up to 23 Tesla.
Single lateral InGaAs quantum dot molecules have been embedded in a planar micro-cavity in order to increase the luminescence extraction efficiency. Using a combination of metal-organic vapor phase and molecular beam epitaxy samples could be produced that exhibit a 30 times enhanced single-photon emission rate. We also show that the single-photon emission is fully switchable between two different molecular excitonic recombination energies by applying a lateral electric field. Furthermore, the presence of a polarization fine-structure splitting of the molecular neutral excitonic states is reported which leads to two polarization-split classically correlated biexciton exciton cascades. The fine-structure splitting is found to be on the order of 10 micro-eV.
We report the investigation of a single quantum dot charge storage device. The device allows selective optical charging of a single dot with electrons, storage of these charges over timescales much longer than microseconds and reliable optical readout of the charge occupancy using a time gated photoluminescence technique. This device enables us to directly investigate the electric field dependent tunneling escape dynamics of electrons at high electric fields over timescales up to 4 us. The results demonstrate that such structures and measurement techniques can be used to investigate charge and spin dynamics in single quantum dots over microsecond timescales.
Anisotropy of spin-orbit interaction (SOI) is studied for a single uncapped InAs self-assembled quantum dot (SAQD) holding just a few electrons. The SOI energy is evaluated from anti-crossing or SOI induced hybridization between the ground and excited states with opposite spins. The magnetic angular dependence of the SOI energy falls on an absolute cosine function for azimuthal rotation, and a cosine-like function for tilting rotation. The SOI energy is even quenched at a specific rotation. These angular dependence compare well to calculation of Rashba SOI in a two-dimensional harmonic potential.
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