Spin transfer and coherence in coupled quantum wells

Spin dynamics of optically excited electrons confined in asymmetric coupled quantum wells are investigated through time-resolved Faraday rotation experiments. The interwell coupling is shown to depend on applied electric field and barrier thickness. We observe three coupling regimes: independent spin precession in isolated quantum wells, incoherent spin transfer between single-well states, and coherent spin transfer in a highly coupled system. Relative values of the interwell tunneling time, the electron-spin lifetime, and the Larmor precession period appear to govern this behavior.