Electron-nuclei interaction in the X valley of (In,Al)As/AlAs quantum dots

Dynamic polarization of electron spins interacting with nuclei in semiconductor nanostructures

“…( 3) we find two parameters: ∆ B = 28 mT and B exch = 5.5 mT. The strength of the hyperfine interaction is in good agreement with measurements of optical spin orientation in transverse and longitudinal magnetic fields in a similar sample [25,30], which supports our interpretation. Using the electron g factor g e = 2 [31,32], we find the splitting between bright and dark states δ 0 = 0.6 µeV.…”

“…Experiment -For experimental demonstration of the suggested mechanism we choose the momentum-indirect (In,Al)As/AlAs QDs. Recently, we showed that in these QDs at low temperatures the exciton spin relaxation is dominated by the hyperfine interaction with ∆ B being a few millitesla [25], while the exciton lifetime reaches hundreds of microseconds [26,27]. The QDs have type-I band alignment (both electron and hole are localized inside the QD) [28,29].…”

Dynamic polarization of electron spins in indirect band gap (In,Al)As/AlAs quantum dots in weak magnetic field: experiment and theory

“…For simplicity we neglect a number of contributions in the Hamiltonian. First, we neglect the long range electron hole exchange interaction, which is suppressed for the indirect excitons [31][32][33] as well as possible noncollinear terms in the short range exchange interaction for electrons in the X valley. We also neglect the hole Zeeman splitting, because the transverse components of the tensor of the heavy hole g factors are very small [34,35], while the longitudinal component does not play a role in the phenomena addressed here [11].…”

“…For simplicity we neglect the nuclear spin polarization [5, 38] and nuclear spin dynamics, which in principle can take place at submillisecond time scale [39][40][41]. Further, we neglect the anisotropy of the hyperfine interaction [33,42], and assume that the distribution function of the Overhauser field has the form [43,44]:…”

“…As a result, the electron g factor equals to 2 in all the QDs. Moreover, since the hyperfine interaction is dominated by the contact interaction with the As nuclei [33], the composition variations in (In,Al)As do not lead to variations of ∆ B . Further, in experiment we detect the PL in a rather narrow window 1.66 − 1.70 eV, which reduces the variance of QD sizes and, as a result, of B ex and ∆ B .…”