Electron-spin relaxation by the interaction with nuclear-spins in InP quantum dots

Effects of nuclear-spins on the electron-spin polarization in singly negatively charged InP quantum dots are studied experimentally at 5 K. Pump-probe photoluminescence measurements of electron-spin relaxation in the microsecond time scale are used to estimate the time period T_N ~ 1 mus of the Larmor precession of nuclear-spins in the hyperfine field of electrons, under the vanishing external magnetic field (B_e,). From the time-integrated measurements of electron-spin polarization as a function of Be applied along the optical excitation axis, we find that the Overhauser field B_N arising from the dynamic nuclear polarization increases linearly with the excitation power (P_X). We obtain B_N =6 mT at P_X = 50 mW. The effective magnetic field of the frozen fluctuations of nuclear- spins is found to be B_F ap 15 mT, independent of P_X .