Homogeneous Linewidth Narrowing Of The Charged Exciton Via Nuclear Spin Screening In An Inas/Gaas Quantum Dot Ensemble

In semiconductor quantum dots, the electron hyperfine interaction with the nuclear spin bath is the leading source of spin decoherence at cryogenic temperature. Using high-resolution two-color differential transmission spectroscopy, we demonstrate that such electron-nuclear coupling also imposes a lower limit for the positively charged exciton dephasing rate, gamma, in an ensemble of InAs/GaAs quantum dots. We find that gamma is sensitive to the energetic overlap of the charged exciton spin states, which can be controlled through the application of an external magnetic field in the Faraday configuration. At zero applied field, electron-nuclear coupling induces additional dephasing beyond the radiative limit and gamma = 230 MHz (0.95 mu eV). Screening of the hyperfine interaction is achieved for an external field of approximate to 1 T, resulting in gamma = 172 MHz (0.71 mu eV) limited only by spontaneous recombination along the dipole-allowed transition. These results are reproduced with a simple and intuitive model that captures the essential features of the electron hyperfine interaction and its influence on gamma.