Dynamics of the electron-nuclear and heteronuclear polarization transfers in optically-oriented semi-insulating InP:Fe

Dynamics of the electron-nuclear and heteronuclear polarization-transfer processes in the optically oriented semi-insulating iron-doped indium phosphide were investigated through the characteristic time scales of the processes. (1) We find in the optical nuclear orientation process that the buildup times for 31P and 115In nuclear polarizations are of the same order. From the analysis of the cross-relaxation process between photo-excited electrons and nuclei, it is concluded that electron-nuclear dipolar-couplings are responsible for the polarization transfer in this case. This example shows that the nuclear-site dependence of the buildup time can be utilized to identify hyperfine couplings responsible for the process. (2) We find in the heteronuclear polarization transfer (cross polarization) process between optically oriented 31P and 115In that the cross-relaxation time is rather short; it is an order of magnitude shorter than that expected for nuclear dipolar couplings when a magnetic field is applied parallel to the crystalline [100] axis. From the cross polarization spectral density analysis, it is concluded that a large J-coupling of the order of 2 kHz exists between these nuclei and that its angular dependence is not of a simple pseudo-dipolar type.