Spin Manipulation and Spin Transport in Semiconductor Two-Dimensional Nanostructures – SpinMan

This project is part of a large effort all over the world to understand and eventually control spin phenomena in semiconductors. A large number of new spintronics devices including spin-transistors, spin-LEDs and spin-lasers have thus been proposed in recent years. Adding the spin degree of freedom in electronics should yield the development of new devices for information technology and solid state quantum information and computation combining the advantages of semiconductors , such as band engineering, growth of epitaxial materials and manufacturing technology of electronic devices. Conduction electron spins are natural candidates for such devices, especially in low-dimensional systems (quantum wells or quantum dots), where electrons can be easily manipulated by external fields or by illumination with light. However, a critical issue in the development of these new semiconductor-based spintronics devices is their ability to operate at room temperature. It is thus crucial to identify materials with sufficiently long electron spin lifetimes at room temperature to process information stored in the form of a high polarisation of spin ensembles. Nevertheless, the longest spin relaxation times of electrons reported so far at room temperature in direct gap bulk semiconductors are rather short, typically a few hundreds of picoseconds. For (110) oriented GaAs semiconductor quantum wells (QW), spin lifetimes as long as 20 ns have been reported at T=300 K as a result of the suppression of the D’Yakonov-Perel-Kochorovskii (DKP) mechanism for electron spins parallel to the growth direction. However this spin relaxation time is strongly anisotropic as it decays down to ~150 ps for electron spins lying in the QW plane. In semiconductor quantum dots, the manipulation and the control of a single electron spin for potential applications in spin electronics and quantum information processing motivates many investigations in Europe, USA and Japan. However these exciting experiments require so far low temperatures (between 100 mK to 10 K depending on the type of quantum dots investigated). In this project, we propose an alternative novel approach based on the control of the Spin-Orbit Coupling (SOC) in GaAs/AlGaAs structures in order to get very long spin lifetimes at room temperature. The spin relaxation and the spin transport will be controlled by manipulating the spin-orbit coupling in semiconductor two-dimensional structures through structural engineering and external electrical field. The project will be done in close collaboration between the Beijing National Laboratory for Condensed Matter Physics (Institute Of Physics, IOP) and the Laboratory of Physics and Chemistry of Nano-Objects (LPCNO) in Toulouse. This joint project includes three tasks: (T1) Growth and technology of GaAs/AlGaAs 2D structures, including the optimization of growth conditions and fabrication of devices (IOP Beijing); (T2) Optical measurement and control of the electron spin dynamics by spin-polarized Time Resolved PhotoLuminescence (LPCNO Toulouse) and Time-Resolved Kerr/Faraday Rotation experiments (IOP Beijing); (T3) Spin transport by Transient Spin Grating (IOP Beijing) and Micro-PL spectroscopy (LPCNO Toulouse).