Effects of External Magnetic Fields on Optical Spin Orientation in GaSe

Abstract

Optical spin orientation experiments have been made in GaSe under longitudinal and transverse magnetic fields at 4.2 K. From the results, the lifetime and the spin relaxation time of the direct exciton are determined to be of the order of 10⁻⁹ s at zero magnetic field. The polarized luminescence spectrum due to the difference of the thermalized populations and that due to the spin memory have been obtained separately under longitudinal magnetic field. This makes it possible for the first time to determine the depolarization factor due to the origins other than the spin relaxation in the emitting state and also the correlation time of the random local field modulation which is responsible for the spin relaxation. Theoretical magnetic field dependence of the degree of polarization of luminescence is derived and compared with experiments for the free exciton line.