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The origin of the ultrafast demagnetisation has been a mystery for a long time. Recently we have proposed an approach based on spin dependent electron superdiffusion. [1-3] A number of experimental works have confirmed the importance and the amplitude of the superdiffusive spin transport for ultrafast magnetisation dynamics [4-7]. In particular the spin superdiffusion model predicted the transfer of magnetisation in the non-magnetic substrate and the possibility of increasing the magnetisation: both phenomena were experimentally confirmed. [4-5]
We predict the possibility of injecting ultrashort (sub-picosecond) spin current pulses from a ferromagnetic metallic layer undergoing ultrafast demagnetisation into a semiconducting substrate. [8] After laser excitation, energetic carriers can overcome the semiconductor bandgap. We address the complex interplay of spin diffusion, the formation of high electric fields at the metal/semiconductor interface, and the concomitant thermalisation of the laser excited carriers by ad hoc numerical techniques. We show that spin currents pulses hundreds of femtoseconds long are injected in the semiconductor and present a record spin polarisation.
Such spin current pulses have the possibility of becoming the carriers of information in future spintronics running at unprecedented frequencies above the THz regime.
[1] M. Battiato, K. Carva, P.M. Oppeneer, Phys Rev. Lett. 105, 027203 (2010).
[2] M. Battiato, K. Carva, P.M. Oppeneer, Phys Rev. B 86, 024404 (2012).
[3] M. Battiato, P. Maldonado, P.M. Oppeneer, J. Appl. Phys. 115, 172611 (2012).
[4] A. Melnikov et al., Phys. Rev. Lett. 107, 076601 (2011).
[5] D. Rudolf, C. La-O-Vorakiat, M. Battiato et al., Nature Comm. 3, 1037 (2012).
[6] A. Eschenlohr,* M. Battiato,* et al., Nature Mater. 12, 332 (2013).
[7] T. Kampfrath, M. Battiato, et al, Nature Nanotechnol. 8, 256 (2013).
[8] M. Battiato and K. Held, Phys Rev. Lett. 116, 196601 (2016).
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