Optical Cooling of Nuclear Spins in a CdTe/CdZnTe Quantum Well: The Impact of Kinetic Local Fields on Cooling Efficiency
Abstract
The efficiency of optical cooling of nuclear spins in a CdTe/CdZnTe quantum well is investigated as a function of an external magnetic field. Our results confirm that there is indeed an optimal external magnetic field for optical cooling. We associate it with the kinetic local field BKL defined by the heating rate of the spin-spin reservoir due to the fluctuations of the hyperfine interaction. We also propose an experimental technique for measuring BKL. For our sample we find that BKL=1.00.4 G and it is independent of the electron polarization and pump power. The measured values of the kinetic local fields are in good agreement with a theoretical calculation BKL = 0.7 G, taking into account indirect spin-spin interactions of Cd and Te nuclear spins and their considerably different hyperfine constants. The hyperfine constants of the magnetic isotopes of Cd and Te in CdTe are estimated.
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