Nuclear-spin effects in singly negatively charged InP quantum dots

Abstract

Experimental investigation of nuclear spin effects on the electron spin polarization in singly negatively charged InP quantum dots is reported. Pump-probe photoluminescence measurements of electron spin relaxation in the microsecond timescale are used to estimate the time-period TN of the Larmor precession of nuclear spins in the hyperfine field of electrons. We find TN to be ∼ 1 µs at T ≈ 5 K, under the vanishing external magnetic field. From the time-integrated measurements of electron spin polarization as a function of a longitudinally applied magnetic field at T ≈ 5 K, we find that the Overhauser field appearing due to the dynamic nuclear polarization increases linearly with the excitation power, though its magnitude remains smaller than 10 mT up to the highest excitation power (50 mW) used in these experiments. The effective magnetic field of the frozen fluctuations of nuclear spins is found to be 15 mT, independent of the excitation power.

Hole-spin initialization and relaxation times in InAs/GaAs quantum dots

“…25 for the C and T h 0 definitions) and has to be compared to the electron spin time at the same scale, T e N ≈hN /A with A the electron hf constant. 18 At low temperature and in the absence of an applied magnetic field, Cheng et al 11 have obtained in interface-fluctuation GaAs QDs T e N = 34 μs, and Pal et al 43 in InP QDs have measured T e N = 1 μs. These values compare well with our experimental determination of T h N because recent studies have shown that C is about ten times smaller than A, 23,[26][27][28] but the interface-fluctuation GaAs and InP QDs are larger than the InAs QDs studied in this work (N is larger).…”

Resonant spin orientation at the exciton level anticrossing in InP quantum dots

“…Fluctuated nuclear hyperfine field B f applied to electrons that we observed in InP QDs is 15 mT, which corresponds to energy change of g e B B f = 1.7 eV for electrons. 20 Therefore, hyperfine interaction between electron and nuclear spins as well as symmetry reduction of QDs from C 2v are the probable origin for the off-diagonal element causing the anticrossing for = 0°. Then, bright excitons mix with dark excitons at B = 1.5 and 2.5 T and strong anticrossings and resonant spin orientation take place.…”

Two-phonon process and hyperfine interaction limiting slow hole-spin relaxation time in InAs/GaAs quantum dots

“…24 Such a behavior of the spin-relaxation time has been observed for an electron confined in InP QDs. 18 There is no theoretical study of the magnetic-field behavior of h 1 , imposed by hf interaction at the μs time scale; such a behavior is then difficult to interpret. As discussed previously, the spin-orbit mechanism is not at the origin of this plateau, but other processes associated with nearby impurities 29 or with the electrostatic environment 30 could be considered.…”

“…1). We measure the second Fourier coefficient of PCD(T L ) as a This approach gives access to a characteristic relaxation time, but not to the full kinetics; nonetheless, the choice of an exponential decay, already observed, 18 appears as well adapted to give the physical trends when an external parameter is applied. Moreover, for the fixed experimental conditions, when compared with a standard pump-probe configuration, the DTS technique gives very similar relaxation time while increasing the signal-to-noise ratio.…”

“…5 Theoretical works also predict that the hf interaction can be at the origin of another slower carrier-spin relaxation time, falling in the microsecond range and related to the nuclear spin-bath dynamics. 3,4,[12][13][14][15][16][17] In this way, at low temperature and in absence of an applied magnetic field, Pal et al 18 have measured an electron-spin relaxation time equal to 1 μs. Moreover, when a magnetic field is applied, the presence of a Zeeman splitting introduces new channels of relaxation via phonon-assisted spin flips mediated by spin-orbit.…”