Electronic spin detection and measurement of spin lifetime in bulk GaAs at room temperature using a highly sensitive radio frequency coil

In this experiment we show the measurement of electronic spin polarization in bulk GaAs using a sensitive rf coil. The basic idea was to excite the electrons from the valence band to the conduction band using a circularly polarized laser. Due to the strong spin orbit coupling in the valence band, a part of the angular momentum of the circularly polarized light is transferred to the electron which allows the excited electron to be spin polarized to certain degree of efficiency, for e.g. 50% for GaAs. The spin of the excited electron decays with a lifetime of about 50ps at 300K. In steady state, for a pump intensity of 100mW at 850nm, a spin polarization density of ∼107 can be achieved in GaAs. These polarized electrons produces a weak magnetization, which was modulated at a frequency of ∼1.8MHz. This generates a varying magnetic field which was detected by a sensitive rf coil of Q-factor ∼33.