Non-equilibrium Overhauser driven hyper-antipolarization
of phosphorous nuclear spins (NEOHAP)

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.

Our recent results on this topic:

D. R. McCamey*, J. van Tol, G. W. Morley, and C. Boehme*
Electronic Spin Storage in an Electrically Readable Nuclear Spin Memory with a Lifetime >100 Seconds
330, 1652 (2010).

D. R. McCamey*, J. van Tol, G. W. Morley and C. Boehme*
Fast nuclear spin hyperpolarization of phosphorus in silicon
Phys. Rev. Lett.
102, 027601 (2009), also on arXiv:cond-mat/0806.3429 (2008).

G. W. Morley*, D. R. McCamey, H. A. Seipel, L.-C. Brunel, J. van Tol, C. Boehme*
Long spin coherence in silicon with an electrical spin trap readout
Phys. Rev. Lett. 101, 207602 (2008), also on arXiv:cond-mat/0806.3431 (2008).

Principal Investigator: Christoph Boehme, Department of Physics and Astronomy, University of Utah,
115 S 1400 E, Salt Lake City, UT 84112-0830, phone 801.581.6806 fax 801.581.4801,
See the University of Utah content disclaimer