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B3: Optical investigation of magneto-electro-optical interactions and their dynamics in oxide heterostructures

Ferroelectric and multiferroic coupling and switching processes, especially their dynamics, shall be investigated by means of time-integrated and time-resolved (down to the ps range) electro-optical ellipsometry. Of interest are the switching processes within a certain material as well as their coupling through interfaces in heterostructures. This coupling causes a volume effect in the adjacent material which can be detected optically and which could be used as electro-magneto-optical switch or rather memory. Remanent optical switching can be induced by the ferroelectric remanence directly or indirectly by the coupling of the ferroelectric polarization and the magnetization.

Regarding the dynamic of the switching processes, three processes, which cover different time scales, are relevant. The optical measurement proofs changes in the electronic system, which occur on a fs time scale and thus follow “instantaneously” the changes of the ferroelectric polarization (ps time scale) or magnetization (up to ns time scale). Of special interest are processes caused in the coupling of the ferroelectric polarization and the magnetization.

For the electro-optical switching, the electrically switchable polarization in ferroelectrica (e.g. BaTiO₃) is used. This ferroelectric polarization causes an electric field which influences the electronic states in an adjacent semiconductor due to band-bending or displacement of free charge carriers, thus influencing the intensity respective the polarisation state of transmitted or reflected light. The electro-magneto-optical switching in ferroelectric-ferromagnetic, ferroelectric-ferromagnetic-semiconducting or multiferroic-semiconducting heterostructures is induced by a magnetization, which is triggered by a ferroelectric polarization, and which causes a spin polarization, either directly in the material or indirectly in an adjacent material. The emerging spin polarisation shall be investigated, and even functionalized, by analysing the intensity respective the polarisation state of transmitted or reflected light. Here, on the one hand, two dimensional electron gases (2DEG) in ZnO quantum wells or at ZnO-MgZnO respective LaAlO₃-SrTiO₃ interfaces, and on the other hand volume materials like zinc-ferrite and zinc-cobaltite are of interest.

Principal Investigators

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