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Final Report Summary - SSM-ILOPSH (Single spin manipulation in locally oxidized p-type semiconductor heterostructures)

Exploring the different relaxation mechanisms leading to spin decoherence and thus the realization of long spin lifetimes in single electron nanodevices is one of the central issues in nowadays spintronics [1]. Although such effects have been widely studied in two-dimensional electron gas (2DEG) based nano-constrictions, the possibility of the utilization of stronger correlation phenomena characteristic to valence band holes on the transport properties of confined two-dimensional hole gases (2DHGs) has remained still unexplored. Recently it has become possible to C-dope (100) AlGaAs heterostructures for high-mobility 2DHG showing clear signatures of the fractional quantum Hall effect. Such structures lend themselves for the fabrication of quantum wires, quantum point contacts (QPCs) and quantum dots (QDs), provided they can be grown close (less than 100 nm) to the sample surface and that stable charging configurations can be obtained.

The proposed project aimed to develop novel schemes for determining spin-related material parameters (g-factor, spin-orbit coupling strength) in various 2DHG nanostructures defined by local anodic oxidation lithography via electrical transport measurements. This is essential in order to explore electron spin dynamics, decoherence and relaxation in QD and double QD semiconductor spin qubits, and to determine conditions for coherent transfer of spin in nano-circuits as well as methods of detection of spin currents. These experiments help to understand and control the coherent spin states of individual charge carriers, which is fundamental for the field of quantum computation in a solid state environment.

In the framework of the project QPCs and QDs were fabricated on a Carbon-doped GaAs/AlGaAs heterostructure grown by D. Reuter and A. D. Wieck at the University of Bochum. The 2DHG is situated 45 nm below the surface. Stable nanoconstrictions tuned by intrinsic in-plane side-gates were patterned by local anodic oxidation lithography carried out by a charged tip of an atomic force microscope (AFM) or, alternatively, by electron beam lithography (EBL) and wet chemical etching.

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