Subsecond nuclear spin dynamics in $n$-GaAs

We use time-resolved detection of the Hanle effect and polarized photoluminescence with dark intervals to investigate the buildup and decay of the spin polarization of nuclei interacting with donor-bound electrons in $n$-doped GaAs. Strong hyperfine coupling defines the millisecond time scale of the spin dynamics of these nuclei, as distinct from the nuclei far from impurity centers, characterized by a thousand times longer spin-relaxation time. The dynamics of spin polarization and relaxation attributed to the nuclei inside the donor orbit is observed on the time scale from 200 to 425 ms.

Figure 1

(a) The PL spectrum of $n$-doped GaAs measured at $B=0$ (solid line) and the spectral dependence of the PL circular polarization degree (crosses). (b) The Hanle curves of $D^{0}X$ line measured for fast polarization modulation $f_{\mathrm{mod}}({\sigma }^{+}/{\sigma }^{-})=50$ kHz at various pumping powers (symbols) and their fitting with Lorentzians. Inset shows the power dependence of the Hanle curve amplitude ${\rho }_0$ (squares) and its fit with an exponential function (line). (c) Power dependence of $B_{1/2}$ (squares) and its linear fit (line). Inset shows the power dependence of the electron spin lifetime (circles) extracted from the HWHM of the Hanle curves and its fit with a rational function (line).

Figure 2

Time dependence of the PL circular polarization degree after demagnetization from the longitudinal $B_z=+2$ mT (blue curve) and $B_z=-2$ mT (red curve) fields in a small transverse magnetic field $B_x=0.5\pm 0.05$ mT and its fitting (solid lines) with Eq. (2).

Figure 3

(a) Schematics of the measurement protocol. (b) Dynamics of ${\rho }_c$ measured for the ${\sigma }^{+}$ and ${\sigma }^{-}$ half periods ($T_{\mathrm{mod}}=1$ s) at different $B_x$ and fixed $B_z=+2$ mT. (c) Hanle curves corresponding to the gated detection in the time intervals shown in panel (b). (d) Magnitude of the Overhauser field, $B_{N0}$, extracted from fitting the Hanle curves (symbols) with Eq. (5) (solid line).

Figure 4

Diagram showing the various components of the electron (a) and nuclear (b) spins in an tilted external magnetic field (the Hanle effect for oblique geometry). The sign of the nuclear field is dependent on the orientation of the pump (${\sigma }^{+}$ or ${\sigma }^{-}$) as follows from the inset of panel (b).

Figure 5

(a) Time dependence of the ${\rho }_c$ for the presence of circularly polarized pump. (b) The Overhauser field values calculated for different dark time intervals using Eq. (6) (squares) and its fitting with an exponential decay function (solid line). Inset shows the temperature dependence of the nuclear spin-relaxation time.