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The magnetic stray field from Fe gates is used to modify the spin precession frequency of InGaAs/GaAs quantum-well electrons in an external magnetic field. By using an etching process to position the gates directly in the plane of the quantum well, the stray-field influence on the spin precession increases significantly compared with results from previous studies with top-gated structures. In line with numerical simulations, the stray-field-induced precession frequency increases as the gap between the ferromagnetic gates is reduced. The inhomogeneous stray field leads to additional spin dephasing. [ABSTRACT FROM AUTHOR]

Electron spins in an InGaAs semiconductor quantum well are used as a magnetometer of magnetic stray fields from patterned Fe stripes. Using time-resolved Faraday rotation, the coherent precession of quantum-well spins in the inhomogeneous field below the Fe stripes is measured for varying magnetic fields. Comparing with reference stripes made of Au, we find an enhancement of the spin precession frequency proportional to the Fe magnetization, in line with a decrease of the spin decay time, which is attributed to the inhomogeneous magnetic stray field in the quantum-well layer. [ABSTRACT FROM AUTHOR]

Aharonov–Bohm oscillations are studied in the magnetoconductance through two micron-sized quantum rings. The structures are defined in a two-dimensional electron gas of a Ga[Al]As heterostructure by way of local oxidation with an atomic force microscope. In the experiments, the rings are used as phase-coherent detectors of the charge state of quantum dots coupled to the rings in two specific arrangements.In the first case, two quantum dots are induced in each of the arms of an open four-terminal ring geometry. This allows to measure the evolution of the relative transmission phase when the number of electrons in each of the dots is tuned using appropriate gate voltages. The experimental findings are compared to expectations from single-particle theory and deviations are discussed.In the second case, a quantum dot is coupled capacitively to one arm of a ring. The amplitude of the Aharonov–Bohm oscillations in the transconductance depends strongly on the charge state of the quantum dot. It is demonstrated that the effect is due to a single-electron screening effect. This shows that Aharonov–Bohm oscillations in a quantum ring can be used for the detection of single electronic charges. [Copyright &y& Elsevier]