Regensburg 2004 – scientific programme

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MA: Magnetismus

MA 31: Spinelektronik

MA 31.1: Talk

Friday, March 12, 2004, 10:45–11:00, H22

Ultrafast Relaxation and Dephasing of Hot Electron Spins in n-GaAs — •Lars Schreiber, Marcus Heidkamp, Bernd Beschoten, and Gernot Guentherodt — II. Physikalisches Institut, RWTH Aachen, 52056 Aachen

Electron spins in n-doped GaAs exhibit longest spin lifetimes (> 100 ns) near the chemical potential for doping concentrations close to the metal-insulator transition [1]. However, the relaxation and dephasing of hot electron spins, which is of interest for spin-tunnel devices [2], is widely unexplored. Therefore, we investigate the relaxation of hot electron spins in n-GaAs for Si doping concentrations ranging from 2 × 10¹⁵ cm⁻³ to 1 × 10¹⁸ cm⁻³ at 6 K and 100 K using two-color time-resolved Kerr rotation utilizing two phase-locked fs-lasers. This set-up allows to coherently pump electron spins with excess kinetic energy and to monitor their intraband relaxation for which the probe energy can be tuned independently.

Ultrafast relaxation (< 10 ps) of hot electron spins into both conduction and donor band states is observed for all samples. Their subsequent dephasing, however, strongly depends on the doping concentration and the pump energy. Only for samples close to the metal-insulator transition (n_c ≅ 2 × 10¹⁶ cm⁻³) spin lifetimes are virtually independent of the pump energy for all temperatures. For the degenerate samples an ultra-fast transfer of spin angular momentum to the total electron sea is observed indicating a collective interaction mediated by electron-electron exchange. Supported by BMBF FKZ 01BM160 and 13N8244

[1] J. M. Kikkawa and D. D. Awschalom, PRL 80 (19), 4313 (1998)

[2] X. Jiang et. al., PRL 90 (25), 256603 (2003)