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The I=1/2 nucleus and the hyperfine coupled donor electron of
phosphorous impurities in silicon produce a four level spin system
whose
phonon driven cross relaxation (Overhauser) rate becomes fast at
intermediate to high magnetic fields. Under illumination of the 31P
-doped crystalline silicon in low bath temperatures (T=1K), a
non-equilibrium is produced in which the phonon temperature is
different from the electron temperature. As excess electrons determine
the longitudinal relaxation of the donor electrons, the both Overhauser
and longitudinal electron relaxation compete for different quasi
equilibria which leads to a rapid pump effect of the nuclear
polarization against the present magnetic field
(hyper-antipolarization). The non-equilibrium Overhauser driven
hyper-anti- polarization of
phosphorous nuclear spin effect (NEOHAP) is important for
initialization of 31P
qubits but also for potential magnetic resonance imaging applications using hyperpolarized solid
state agents. The experimental work the NEOHAP effect is
done in collaboration with the EMR group of the National
High Magnetic Field Laboratory in Tallahassee, Florida. |
 Electrically
detected magnetic resonance spectrum of Si:P at T = 1.37 K under
illumination. The nuclear polarization determined by comparing the area
of the hyperfine split resonances is P = −68 ± 1%. This
polarization was pumped from equilibrium within less than 10 minutes. |
 a)
Sketch of the energy levels of the four spin eigenstates of a
phosphorus donor atom in silicon in presence of very high magnetic
fields indicate allowed relaxation transitions b) Sketch of the change
from a thermally polarized spin ensemble to a hyperpolarized spin
ensemble for a large phonon temperature and a low electron temperature.
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Our recent results on this topic: D. R. McCamey*, J. van Tol, G. W. Morley, and C. Boehme*
D. R. McCamey*,
J.
van Tol, G. W. Morley and C. Boehme*
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