Temporally and spatially resolved ballistic pure spin transport

The ballistic movement of spin-polarized electrons in a semiconductor is spatially and temporally resolved. Pure spin currents are injected into GaAs quantum wells at 800.3em0exK by optical quantum interference processes, and the subsequent ballistic transport is measured by pump-probe techniques having ~2000.3em0exfs temporal and ~10.3em0exnm spatial resolution. An average injection velocity of ~500.3em0exnm∕ps and spin momentum relaxation times ranging from 1.2 to 0.60.3em0exps are extracted for carrier densities varying from 1.5 to 12×10¹⁶0.3em0excm^-3 when the electrons are excited into the conduction band with excess energy ~250.3em0exmeV, less than that of one optical phonon.