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Oxide-based memristive devices, which exhibit two or more resistive states under electrical biasing, are promising candidates for future non-volatile memories as well as for active elements for neuromorphic computing. It has become widely accepted that memristive switching in oxides is in most cases connected with a voltage-driven oxygen vacancy movement and a resulting metal-to-insulator transition. However, the current knowledge of the microscopic details is very limited so far. One of the obstacles for its further elucidation has been that the net changes of the atomic and electronic structure during memristive switching are very small and occur primarily at the electrode interface or within nanoscale filaments. By employing different approaches of X-ray based spectromicroscopy, we could prove the formation of an oxygen vacancy enriched filament in epitaxial SrTiO3 thin film devices, which occurs preferentially at preformed positions such as extended defects. For high current operation, electric biasing goes along with the formation of SrO at the electrode interface which has a significant impact on the stabilization of the resistance states of the devices. In operando studies of SrTiO3 devices with photoelectron-transparent graphene electrodes enabled us to detect reversible changes of the O K-edge spectra within spatially confined regions of the devices. Based on these results, we obtain for the first time a quantitative estimate of the amount of oxygen vacancies shifted during the switching process.

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Regina Dittmann, Forschungszentrum Juelich
Seminar room of the Institute of Physics II
Contact: not specified