Spin flip Raman scattering in low dimensional semiconductors

Abstract

The research field of spintronics, combining the advantages of both the intrinsic charge and spin, attracts considerable interests. It aims at the full control over the quantum mechanical nature of the spin. However, fundamental questions are challenging the semiconductor spintronics, e.g., the dimension of the semiconductor as well as the limitation of the quantum state lifetime or the loss of coherence by perturbing interactions within the semiconductor structure are crucial parameters. The challenges for achieving novel spin effects or improving existent spin phenomena are based on interaction, namely interactions between carriers themselves as well as a carrier and a second system, such as the nuclear spin or phonon system leading to a scattering process and thus to spin decoherence. By means of the resonant spin-flip Raman scattering technique fundamental spin interactions of carriers confined in low-dimensional semiconductors, their dependence on the local structure symmetry as well as the type and excitation state of the carrier complex are characterized. It is shown that the scattering processes of the electron, hole, and exciton spins depend on the symmetry of the crystal lattice, quantum confinement potential, and magnetic field confinement. In the studied quantum well structure the anisotropic exchange interaction is dominant, while the isotropic exchange interaction and the carrier scattering via an acoustic phonon represent the main spin-flip scattering mechanisms in the studied quantum dots. Moreover, the light-heavy-hole mixing induced by strain and/or shape anisotropies, the level mixing resulting from the coupling of a tilted magnetic field to a nonzero in-plane magnetic moment of the electron and/or heavy-hole, the coupling between the ground and excited electron states, as well as the electron-nuclear hyperfine interaction in quantum dot ensembles are studied with regard to the spin-flip Raman scattering. The studies outline problems of the semiconductor spintronics, but also ways to identify and monitor them, and present a novel quantum dot structure providing a long exciton lifetime and temperature-robust longitudinal spin relaxation time thus making a step toward the realization of spin-based applications.