Ultrafast spin injection in semiconductors - Fritz Haber Institute

Fritz-Haber-Institut der Max-Planck-Gesellschaft
Physikalische Chemie — Direktor: Prof. Dr. Martin Wolf
Department Seminar:
Monday, May 2, 2016, at 11:00 a.m.;
— all are invited to meet at around 10:40 for a chat and coffee —
Short introductory talk (15 min.):
Tom Seifert
Terahertz Physics Group, PC Dept., FHI Berlin.
Spintronic emitters of terahertz radiation
Main talk:
Dr. Marco Battiato
Computational Materials Science group,
Institute of Solid State Physics, Vienna University of Technology.
Ultrafast spin injection in semiconductors
Richard-Willstätter-Haus, Faradayweg 10
T Kampfrath
Abstract of main talk:
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. In particular the spin superdiffusion model predicts the transfer of magnetisation
in the non-magnetic substrate and the possibility of increasing the magnetisation: both phenomena were
experimentally confirmed [4-5].
Here we predict the possibility of injecting spin from a ferromagnetic metallic layer undergoing
ultrafast demagnetisation into a semiconducting substrate. After laser excitation, energetic carriers can
overcome the semiconductor bandgap. However due to the simultaneous injection of spin and charge and
the superdiffusive nature of the transport, the underlying mechanism of the spin injection becomes very
complex. In this theoretical work we model these dynamics in a Ni/Si sample and we show how within
the first hundreds of femtoseconds a considerable amount ofspin can cross the metal-semiconductor
interface. The injected spin moment is found to be orders of magnitude larger than what can currently be
injected in semiconductors by standard steadystate techniques.
If our prediction will be verified experimentally, it could bridge magnetisation dynamics in metals
and spin transport in semiconductors, the latter being the most important building blocks of modern
electronics. In the future this could bring ultrafast magnetisation dynamics closer to fast spin-transport in
semiconductors leading to technologically feasible ultrafast spintronics.
Co-author: Karsten Held
[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, et al., Nature Comm. 3, 1037 (2012).

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