Gating carrier spin dynamics in coupled quantum wells

In appropriately designed GaAs/AlGaAs coupled quantum wells (CQWs) optically generated excitons can be made direct or indirect depending on local electric fields. We investigate the electron spin dynamics of CQW systems using an externally controlled electric field to enhance or diminish the overlap of exciton electron and hole wave functions. Time-resolved Faraday rotation experiments reveal an abrupt and significant enhancement of the electron spin lifetime T2* as a function of applied gate voltage. This enhancement occurs without any change in electron g-factor suggesting the suppression of a spin decoherence mechanism. Photoluminescence experiments show that the enhancement occurs at the bias voltage threshold between direct and indirect exciton ground states. Nuclear spin is also studied in the CQW system where we examine the gate induced nuclear resonance mechanism reported previously.