Optical detection of electron spin dynamics driven by fast variations of a magnetic field: a simple method to measure T_1, T_2, and T_2^* in semiconductors

Abstract

We develop a simple method for measuring the electron spin relaxation times T_1, T_2 and T_2^* in semiconductors and demonstrate its exemplary application to n-type GaAs. Using an abrupt variation of the magnetic field acting on electron spins, we detect the spin evolution by measuring the Faraday rotation of a short laser pulse. Depending on the magnetic field orientation, this allows us to measure either the longitudinal spin relaxation time T_1 or the inhomogeneous transverse spin dephasing time T_2^*. In order to determine the homogeneous spin coherence time T_2, we apply a pulse of an oscillating radiofrequency (rf) field resonant with the Larmor frequency and detect the subsequent decay of the spin precession. The amplitude of the rf-driven spin precession is significantly enhanced upon additional optical pumping along the magnetic field.