Coherence and phase control of electrically injected spins

using ultrafast current pulses

L. Schreiber¹, J. Moritz¹, C. Schwark¹, B. Beschoten¹, G. Güntherodt¹, X. Lou², P. Crowell², C. Adelmann², C. Palmstrøm³

¹ II. Physikalisches Institut, RWTH Aachen University, 52056 Aachen and Virtuelles Institut für Spinelektronik (VISel)

²School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA

³Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN, USA

Efficient electrical spin injection from a ferromagnet into a semiconductor has been demonstrated for various material systems by steady-state experiments. We introduce a novel time-resolved technique based on electrical pumping and optical probing. As a pump we apply ultrafast current pulses (~ 200 ps) to electrically inject spin packets from an iron layer through a reverse biased Schottky barrier into an n-GaAs layer. Spin coherence in the semiconductor is probed by subsequent spin precession in a transverse magnetic field using time-resolved Faraday rotation. We observe spin precession for current pulse widths down to 200 ps. The spin polarization of the spin packets is directly measured by Faraday rotation and is found to increase linearly with the current pulse width for pulses shorter than 3 ns at small magnetic fields. This finding together with independent measurements of the samples' high frequency bandwidth indicate that even shorter than 200 ps pulses might be used for generating coherent spin currents in our devices. - Work supported by BMBF, DFG and HGF.