Extended pump-probe Faraday rotation spectroscopy of the submicrosecond electron spin dynamics in n -type GaAs

Abstract

We develop an extended pump-probe Faraday rotation technique to study submicrosecond electron spin dynamics with picosecond time resolution in a wide range of magnetic fields. The electron spin dephasing time T * 2 and the longitudinal spin relaxation time T1, both approaching 250 ns in weak fields, are measured thereby in n-type bulk GaAs. By tailoring the pump pulse train through increasing the contained number of pulses, the buildup of resonant spin amplification is demonstrated for the electron spin polarization. The spin precession amplitude in high magnetic fields applied in the Voigt geometry shows a non-monotonic dynamics deviating strongly from a mono-exponential decay and revealing slow beatings. The beatings indicate a two spin component behavior with a g-factor difference of ∆g ∼ 4 × 10 −4 , much smaller than the ∆g expected for free and donor-bound electrons. This g-factor variation indicates efficient, but incomplete spin exchange averaging.doi:10.1103/PhysRevB.94.241202Initialized electron spins in semiconductors undergo a complex dynamics depending on external magnetic field, interaction with other charge carriers and nuclei, spinorbit interaction, etc. Knowledge of the resulting spin dynamics provides information on these interactions and related spin properties such as g factors and relaxation times which are important for basic research and application in information technologies. Commonly, information on spin properties is mostly obtained from resonance techniques like electron paramagnetic resonance, optically-detected magnetic resonance, spin-flip Raman scattering, or polarized photoluminescence (Hanle effect). The development of pump-probe Faraday/Kerr rotation spectroscopy has facilitated exploration of the coherent spin dynamics, in particular the Larmor spin precession around a magnetic field, with picosecond temporal resolution and opened new ways for spin control and manipulation [1][2][3][4][5].The main limitation imposed on the standard pumpprobe technique is the restricted time range that can be monitored. This restriction comes from the finite length of mechanical delay lines for the pump-probe delay limiting this time range to a few nanoseconds, which can be too short to address the carrier spin dynamics in semiconductors. To evaluate longer spin dephasing times the resonant spin amplification (RSA) technique [6,7] can be used, which, however, does not provide detailed insight into complex spin dynamics such as a nonexponential decay of spin polarization. Also, the longitudinal spin relaxation characterized by the T 1 time typically exceeds the nanosecond range, so that indirect optical techniques like the spin inertia method [8] have to be used, again with limited access to nontrivial spin dynamics.Here we extend the standard pump-probe Faraday rotation (PPFR) technique to address a much longer time range by employing a tailored pump pulse sequence, while maintaining picosecond time resolution. The technique is applied to the submicrosecond electron spin dynamics in bulk n-type ...

Radiofrequency driving of coherent electron spin dynamics inn-GaAs detected by Faraday rotation

“…This decay is similar to the spin dynamics measured by the extended all-optical pump-probe Faraday rotation method, using the same experimental conditions [ Fig. 1(d)] [4]. Interestingly, the increase in the spin precession amplitude with time is determined by T 2 following the equation: 1 − exp(−t/T 2 ).…”

“…The method of rf spin pumping and optical probing, developed in this work, is inspired by the similar alloptical pump-probe technique [1][2][3], and in particular by the extended pump-probe method [4], in which electron spins are oriented by circularly-polarized laser pulses. By contrast, the rf pump directly addresses the resident electron spins at their Larmor precession frequencies, which is likely advantageous compared to optical pumping at the much higher frequencies of the resonant electron transitions, unrelated to the spin precession.…”

Increased sensitivity of spin noise spectroscopy using homodyne detection in n -doped GaAs

“…A spin relaxation time of = (2 Γ HWHM ) −1 = 52 ns is obtained at the lowest density of excitation, which is comparable with measurements of the same sample using the Hanle effect [31]. In contrast, in an extended pump-probe experiment [37,38], the spin relaxation time reaches values of (2 Γ 0 ) −1 = 90 ns under similar optical excitation conditions of the same sample. Note that in this case, the optically excited electron spins evolve in the darkness between the arrival of the pump and probe pulses.…”

Electron and hole spin relaxation in InP-based self-assembled quantum dots emitting at telecom wavelengths

“…In a longitudinal magnetic field B F , the spin polarization decays monotonically without oscillations [36,45]. In high enough B F , this decay is characterized by a fast component with decay time 0.6 ns, close to the exciton lifetime, and a slow component of somewhat smaller amplitude.…”