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Physical Society Colloquium
Dr. Jay Kikkawa
Department of Physics Although quantum mechanics plays an important role in today's semiconductor electronics, the use of solid state quantum coherence for device applications remains largely undeveloped. Here, we discuss recent progress in the use of n-type semiconductors for the storage and transport of electronic spin coherence. We modify the technique of time-resolved optical Faraday rotation to accommodate doped semiconductors with enduring spin memories, revealing a dramatic dependence of extra-electronic spin decoherence on carrier density. In low-doped GaAs crystals, we find a regime in which such decoherence times exceed 100 nanoseconds and show an unusual power-law divergence as the ambient magnetic field strength approaches zero. These long decoherence times allow one to amplify electronic spin polarization tenfold by driving collective magnetic oscillations into resonance with a periodic optical excitation. Space-time mapping of spin motion then shows that an applied electric field can be used to deconstruct these resonances, exploiting a weak entanglement of orbital and spin motion to effect spin-polarized transport over macroscopic distances.
Thursday, January 28th 1999, 16:00 |