Optical detection of electron spin dynamics driven by fast variations of a magnetic field: a simple method to measure $$T_1$$T1 , $$T_2$$T2 , and $$T_2^*$$T2? in semiconductors

摘要

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.