Fast Nuclear Spin Hyperpolarization of Phosphorus in Silicon

E. Sorte, W. Baker, D.R. McCamey, G. Laicher, C. Boehme, B. SaamDepartment of Physics, University of Utah

Silicon doped with Phosphorus

Introduction

Introduction

H0

Energy Splitting in Magnetic Field

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ms = 12 ,mI = 1

2

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ms = − 12 ,mI = 1

2

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ms = − 12 ,mI = − 1

2

€

ms = 12 ,mI = − 1

2

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ˆ H = −μ e ⋅Ho − μN ⋅Ho + AI ⋅J

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Tx =1

Γx=

4πh2s5ρ

ω02kTresγ

2IA2

• Tx returns the spin populations n2 and n3 to thermal equilibrium with the phonon reservoir

1 D. Pines, J. Bardeen, C. Slichter, Phys. Rev. 106, 489 1957

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1

Tx

=2π

h

dk

2π( )3∫ δ hsk − hω0( ) Nk +1 1

2 δA Nk

2

Relaxation Times

n4

n3

n2

n1

1

1X

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T1 =1

Γ1

∝ e−

E

kTspin

€

⇒

but

• T1 returns the spin populations n4 and n3 / n1 and n2 to thermal equilibrium with the lattice

Ee ≈ 240 GHz (electric Zeeman)

En ≈ 147 MHz (nuclear Zeeman)

A ≈ 117 MHz (hyperfine interaction)

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ωconduction band

valence band

phonons

Tspin (LH2 bath)

Tres

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hω > E res > kTspin

In general: Tres ≠ Tspin

Tres > TspinIn fact we want:

Temperature

• Constant illumination generates new charge carriers, leading to steady state with constant density of “hot” electrons

• As hot electrons cascade toward the lattice temperature, they emit phonons at constant rate.

G.Feher, Phys. Rev Lett 3, 135 (1959)

B=8.5T

Mechanism

B=8.5T

X

Mechanism

B=8.5T

X

1

1

Mechanism

X

B=8.5T

1

1

Mechanism

X

B=8.5T

1

1

Mechanism

X

B=8.5T

1

1

Mechanism

X

B=8.5T

1

1

Result = net nuclear antipolarization:

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P =(n1 + n2) − (n3 + n4 )

(n1 + n2) + (n3 + n4 )

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Tres >> Tspin

Mechanism

Experimental - EPR

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Tx =1

Γx=

4πh2s5ρ

ω02kTresγ

2IA2

EDMR at T = 1.37 K Xe discharge lamp

EDMR at different temperatures

Experimental - EDMR

D. R. McCamey, J. van Tol, G. W. Morley, C. Boehme, eprint arXiv:0806.3429v1 (2008)

Conclusion

• NMR on 31P nucleus to actually “see” the nuclear polarization.

Future Experiments

Comparison of polarization measured using EDMR vs EPR at different intensitiesof light (Hg discharge) at T = 3 K.

Hg discharge has higher spectral temperature, yielding higher polarizations(P=-24% at 3K vs -6% at 3K for Xe lamp) independent of intensity for most part.

Polarization with ESR 45% that measured with EDMR

Experimental - EDMR vs. ESR