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Optical Pump-Probe Detection of Coherent Nuclear Spin Dynamics
in n-GaAs (110) Quantum wells |
We
demonstrate local manipulation and detection of nuclear spin coherence in
semiconductor quantum wells by an optical pump-probe technique combined with
pulse rf NMR. The Larmor precession of photoexcited
electron spins is monitored by time-resolved Kerr rotation (TRKR) as measure of
nuclear magnetic field. Under the irradiation of resonant pulsed rf magnetic fields, Rabi
oscillations of nuclear spins are traced by TRKR signals. The intrinsic
coherence time evaluated by a spin-echo technique reveals the dependence on the
orientation of the magnetic field with respect to the crystalline axis as
expected by the nearest neighbor dipole-dipole interaction.
%20Quantum%20wells.files/image003.gif)
|
Figure 1 |
(a) The experimental setup of NMR
by optical pump-probe detection with a rf coil. (b) The NMR spectra appeared in TRKR signal: The
data were obtained at Δt = 640 ps with Brf
at 8.18 MHz. (c) Close view of the NMR spectra (b) in the vicinity of 71Ga
resonance (ΔB = B - 0.630 T)
(d) The electron Larmor precession at B = 0.630 T with and without applying Brf. |
%20Quantum%20wells.files/image005.gif)
|
Figure 2 |
Optically
detected Rabi oscillation of 71Ga: (a) grayscale plot of TRKR
signals ( at Δt = 640 ps) when a pulse Brf with t(rf) is applied at tlab
= 0 s. (b) θK for t(rf) = 16 ms is plotted as
a function of tlab.
(c) ΔθK defined in (b) is plotted as a function of t(rf), representing the Rabi
oscillation of 71Ga. A solid curve is the fitted result. |
%20Quantum%20wells.files/image007.gif)
|
Figure 3 |
(a)
Brf pulse
sequences for observation of quantum coherence of nuclear spin (71Ga)
are shown. (b) The changes in TRKR signal ΔθK after
application of the pulse sequences (A), (B) and (C) plotted as a function of
the time interval t.
The result of (B) (spin echo) gives the intrinsic coherence time T2 of 71Ga. |
%20Quantum%20wells.files/image009.gif)
|
Figure 4 |
(a)
The cw-NMR spectra of 71Ga measured at α
= 45° detected by TRKR. ΔB = B - 0.630 T and Δt = 280 ps. Compared to result in Fig. 1(c) for α = 4°, the line width becomes broader by a factor of 2.5. (b) The Rabi
oscillation obtained by pulse NMR at α = 45° is plotted by closed
circles. A solid curve is the fitted result. The decay constant T2Rabi ~ 220 ms becomes also shorter than 480 ms
for α = 4°. By spin-echo measurements at α = 45° (not shown), we obtained T2 = 100 ms and T2* = 60 ms,
respectively, both of which are about 1/2 ~ 1/3 of those for α = 4°. This decrease of coherence by tilting B
with respect to the crystalline axis of the sample can be understood by the
enhanced dipole-dipole interaction. |
| Related publication: |
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| (1) H. Sanada, Y. Kondo, S. Matsuzaka, K. Morita, C. Y. Hu, Y. Ohno and
H. Ohno, Phys. Rev. Lett. 96, 067602 (2006) |
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