Extended pump-probe Faraday rotation spectroscopy of the submicrosecond electron spin dynamics in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>n</mml:mi></mml:math>-type GaAs

Abstract

Pump-probe Faraday/Kerr rotation spectroscopy is a powerful tool for exploring the coherent spin dynamics with picosecond temporal resolution. However, this has so far been possible only in time ranges up to a few nanoseconds. In this work, the technique is extended to address time ranges orders of magnitude longer by employing a tailored pump and probe pulse sequence, while maintaining picosecond time resolution. The submicrosecond electron spin dynamics in $n$-type GaAs with doping concentrations close to the metal-insulator transition can be directly accessed thereby with high precision, rendering the electron spin dephasing time ${T}_{2}^{*}$ and the longitudinal spin relaxation time ${T}_{1}$. Both approach 250 ns in weak magnetic fields. The Larmor spin precession in high magnetic fields applied in the Voigt geometry shows nonmonotonic dynamics deviating strongly from a mono-exponential decay and revealing $g$-factor variations on the level of 10${}^{-4}$, demonstrating the high precision of the method. The possibility of varying the pump pulse train composition from single to multiple pulses provides detailed insight into the synchronization of the spin precession in the electron gas when subject to periodic laser excitation.