J.S. Colton, ODMR studies of n-GaAs Optically-detected magnetic resonance studies of n-GaAs Talk for APS March Meeting, Mar 20, 2009 John S. Colton, Brigham Young University Undergraduate students: Benjamin Heaton Michael Johnson Daniel Jenson Mitch Jones Steve Brown Samples provided by Allan Bracker, Naval Research Laboratory Berry Jonker & Aubrey Hanbriki, also NRL Funding: National Science Foundation
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J.S. Colton, ODMR studies of n-GaAs Optically-detected magnetic resonance studies of n-GaAs Talk for APS March Meeting, Mar 20, 2009 John S. Colton, Brigham.
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J.S. Colton, ODMR studies of n-GaAs
Optically-detected magnetic resonance studies of n-GaAs
Talk for APS March Meeting, Mar 20, 2009
John S. Colton, Brigham Young UniversityUndergraduate students: Benjamin Heaton
Michael JohnsonDaniel JensonMitch JonesSteve Brown
Samples provided by Allan Bracker, Naval Research LaboratoryBerry Jonker & Aubrey Hanbriki, also NRL
Funding:National Science Foundation
J.S. Colton, ODMR studies of n-GaAs
Outline
• Samples• Electron spins in n-GaAs: some basics• ODMR
proportional to polarization angle proportional to spin polarization
J.S. Colton, ODMR studies of n-GaAs
Various optical powers
What’s going on?• Electron spins polarize the nuclei (when taken out of equilibrium)• Nuclear spins produce Beff
“Probe” is affecting system
Typical ODMR peak• QW sample• width: T2
* 10-15 ns
J.S. Colton, ODMR studies of n-GaAs
Microwave pulses needed to (hopefully) control spins
Problems: (1) Lockin response limited to 100 kHz (10 ms) (2) Need to use as little laser power as possible
Solutions: • use boxcar integrators gated signal detection • use pulsed light in addition to pulsed microwaves
Signal = BC1 – BC2
Later: BC2 not always needed
J.S. Colton, ODMR studies of n-GaAs
Pulsed Microwaves, cw light
Boxcar can be as good as lockin possibly better
Allows for very short pulse lengths, little loss of S/N
Still see ODMR peaks down to 10 ns gates!
J.S. Colton, ODMR studies of n-GaAs
Pulsed Light (pulsed microwaves, too)
• Why the difficulty?– Our current idea: the vast difference in signal between light
on/light off is “leaking through” the boxcar somehow– Limited success came only when light pulses long enough that
we could filter out that component of the signal and leave behind the faster response to microwaves
• Requiring that long of light pulses ruins the major benefit• Giving up nice idea…for now
J.S. Colton, ODMR studies of n-GaAs
Spin LED
• Iron spin contact– Spin polarized electrons into 10 nm QW
• Substantial optical/spin polarization when B 2 T• Eliminates probe beam altogether!• Also: doesn’t rely on low T to initialize spin• Experiments planned for immediate future
Image from Jonker, Proc IEEE 2003
J.S. Colton, ODMR studies of n-GaAs
Conclusions/What’s next?
• Much successful ODMR in GaAs, 8.5-12 GHz, using: – Resonant cavity– Kerr rotation detection
• Looking for coherent oscillations (next talk)• Dealing with strong nuclear effects (next talk)