Non-charge-carrier-mediated spin-transport in an organic semiconductor*

We report experiments scrutinizing existing theoretical pictures of spin-transport in organic thin films, based on the idea that this is due to the same mechanisms as charge transport [1, 2], as it is the case for many inorganic materials. Experimentally, we used the inverse spin-Hall effect (ISHE) in thin Pt films [3] to detect pure spin currents in adjacent organic semiconductor (Alq₃) layers, caused by ferromagnetic resonance driven spin-pumping of NiFe layers. To verify the involvement of charge carrier spins, the I_ISHE is expected to vanish when the charge carrier spins in Alq₃ are magnetic resonantly scrambled [4]. No such quenching of I_ISHE is observed though within the given noise thresholds, indicating that spin-transport is neither due to charge carriers propagation nor due to spin-spin coupling. We discuss our experimental findings and various control measurements to corroborate the results. [1] M. Groesbeck et al. Phys. Rev. Letts. 124, 067702 (2020); [2] Z. Yue et al., Phys. Rev. B 92, 045405 (2015); [3] K. Ando et al. Nat. Phys. 12, 622 (2013); [4] H. Popli et al. Phys. Rev Appl. 14, 034012 (2020).