Spin and energy relaxation of excitons in GaAs coupled quantum wells

ORAL

Abstract

We report sub-100ps exciton spin relaxation and transient splitting attributed to exchange interaction for intra-well excitons. The spin splitting and relaxation are analyzed in terms of inter-exciton and intra-exciton exchange interaction. For inter-well excitons where intra-exciton change interaction is suppressed, a spin decay-time $>$1-ns is observed at low densities. Transient exciton spin splitting and relaxation are determined from time-resolved photoluminescence (TRPL) spectroscopy and polarimetry with a streak camera system. In contrast to standard TRPL measurements based on up-conversion and pump-probe techniques, the streak-camera setup allows for speedy spectroscopy and Stokes polarimetry measurements as a function of the exciton density, and magnetic and electric fields. For 6- nm GaAs/AlGaAs quantum wells at intermediate density (a few 10$^ {10}$ cm$^{-2})$, a spin splitting of 2-meV with a decay time of $\sim$50 ps appeared instantly under a near-resonant ps pulsed excitation. For long-lived ($>$1ns) inter-well spatially indirect excitons under a cross-well electric field, intra- exciton exchange interaction is suppressed and the inter-exciton interaction is dominantly dipolar. Transient exciton energy shift and spin relaxation are characterized versus the exciton density and applied electric field under an excitation near the intra-well direct exciton transition.

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Authors

  • Chih-Wei Lai

    Michigan State University

  • J.A. Summers

    Duke University Medical Physics Graduate Program, Southwest Research Institute, Kettering University, Department of Physics and Astronomy, Wayne State University, Wayne State University, University of Nebraska, University of Stockholm, University of Michigan-Dearborn, Wayne State University, Detroit, MI, Cornell Univ., Air Force Research Labs, Univ. Akron, National Center for Manufacturing Sciences (NCMS), Youngstown State U, Dept. Physics, Department of Natural Sciences, University of Michigan-Dearborn, Department of Physics and Astronomy, Wayne State University, Detroit, Bhabha Atomic Research Centre, Hyderabad, India, NIST Center for Neutron Research, NIST, Gaithersburg, Maryland, Max Planck Institute for Solid State Research, Michigan State University

  • J.A. Summers

    Duke University Medical Physics Graduate Program, Southwest Research Institute, Kettering University, Department of Physics and Astronomy, Wayne State University, Wayne State University, University of Nebraska, University of Stockholm, University of Michigan-Dearborn, Wayne State University, Detroit, MI, Cornell Univ., Air Force Research Labs, Univ. Akron, National Center for Manufacturing Sciences (NCMS), Youngstown State U, Dept. Physics, Department of Natural Sciences, University of Michigan-Dearborn, Department of Physics and Astronomy, Wayne State University, Detroit, Bhabha Atomic Research Centre, Hyderabad, India, NIST Center for Neutron Research, NIST, Gaithersburg, Maryland, Max Planck Institute for Solid State Research, Michigan State University