Interface-sensitive study of ultrafast spin dynamics in multilayer semiconductors

We report the first application of pump--probe second harmonic generation (SHG) measurements to characterize optically induced magnetization in non-magnetic multilayer semiconductors GaAs/GaSb/InAs. A circularly-polarized pump beam has been used to inject electrons into the conduction band of GaAs, where the photons impart their angular momentum to electron-hole pairs. Because of the interface-sensitive method, the spins accumulated at the GaSb/InAs interface have been monitored. Subsequent precession of these spins about the applied magnetic field has then been detected by a time-delayed probe pulse as an interfacial magnetic field induced SHG response. The electron and spin transport through the heterostructure takes place on the time frame of 15-20 ps, and it is followed by the relaxation of interfacial magnetic and electric fields on the time scale of 100 ps.