The Importance of Spinterfaces for Organic Spintronics
Dr. Mirko Cinchetti (Univ. Kaiserslautern)

Interfaces between ferromagnetic materials and organic semiconductors – also known as spinterfaces - constitute an incredibly rich playground in the field of spintronics. For example, spinterfaces have the potential to be implemented as tunable spin filters [1,2], which will pave the way to a whole new class of advanced, i.e., actively controlled spintronics devices. The progress in the field of spinterface science depends thus critically on elucidating the still unexplored spin-dependent carrier dynamics at such hybrid interfaces.
We show here with spin- and time-resolved two-photon photoemission (2PPE) that we can access the dynamics of the relevant hybrid electronic interface structure that determines the spin-filtering efficiency. In a real-time pump-probe experiment, we follow the spin-dependent trapping of excited electrons at the prototypical interface between the ferromagnet cobalt and the metalorganic complex tris-(8-hydroxyquinolinato) aluminium (Co-Alq3 interface). As schematically shown in the figure, in our 2PPE experiments the pump photon is used to populate an unoccupied hybrid state at the Co-Alq3 interface with a transient spin-polarization. The transiently populated hybrid state is probed by analyzing the photoemitted electrons with respect to their kinetic energy, spin and momentum. This gives access to the relevant transient femtosecond-to-picosecond electron dynamics in the hybrid interface state that eventually determine the spin filtering efficiency of the spinterface. We observe a substantial spin-dependent confinement of electrons at the interface [3]. Such spin-dependent trapping behavior elucidates the fundamental microscopic origin of the spin-filtering properties at spinterfaces, which is important for the design of next-generation spintronics devices based on tunable organic spin filters.