Figure 2: Observation of overhauser shift at RT.
From: Efficient room-temperature nuclear spin hyperpolarization of a defect atom in a semiconductor
(a) A schematic picture of the experimental configuration, where the optical excitation and photoluminescence detection are indicated by the red and black arrows, respectively. The modulation scheme of the excitation light, at a modulation frequency of 135 Hz, is also shown. (b) A pseudospin description of the optically pumped electron spin S0 and its projection Sz under a combined effect of a fluctuating effective magnetic field BF, a longitudinal external magnetic field Bz and an optically induced nuclear field BN. (c) The total intensity of the band-to-band photoluminescence as a function of Bz under σ+ (the blue curves) or σ− (the red curves) excitation (denoted by 
), with respect to that under linear (σx) excitation (
), obtained at RT from GaN0.013As0.987 after rapid thermal annealing treatment. The excitation wavelength was 930 nm, and excitation power levels were 150 and 30 mW. The solid green lines are Lorentzian fits of the experimental curves. (d) The absolute values of an average nuclear field (
) and the corresponding PN of the Gai defects, as a function of optical pumping power for the specified GaNAs epilayers. The open symbols represent the experimental data. The dashed lines are calculated values obtained from a rate equation analysis, with the specified key fitting parameters. Other fitting parameters are T1SC=5 ns and τN=10 ns. The deduced difference in the e–n spin flip-flop time τA between the two samples is consistent with what is expected from the difference in the HF coupling constant A of the Gai defects present in these samples.
