1140.120.11.120
Probing Semiconductor Nanostructures by a Pulsed Phase-Lock-Loop System
Yuen-Wuu Suen
Department of Physics, National Chung Hsing University
孫允武中興大學物理系
2140.120.11.120
OUTLINES
1. How it works
2. The home-brewed pulsed phase-lock-loop system
3. Some preliminary results for two-dimensional electron systems (2DES)
4. What can we do next?
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Detection by Phase Lock Loop (PLL)
phase=1=11PLL system
s=ss
0 =1+ s =11+s(B)s
0 =0 (by tuning )=1+ s(B) =11+s(B)s
=1/1+s(B)s
B:the parameter (magnetic field, excitations, temperature, etc) changed in the experiment
can be measured very accurately.
sample
known
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Type-II PLL
Sample under detection
Sample under detectionSAW Delay-LineCoplanar Waveguide (CPW)
Basic scenario
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2
2
00 )/(1
1
2 Mxx
effK
Lf
f
σ
2
2
SAW )/(1
/
2 Mxx
MxxeffKk
σσσσ
L
)( 210 M
GaAs:3.6×10-7 -1
GaAs/LiNO3(Y-Z):1.8×10-6 -1
2
,2, 00 fq xxxx
SAW Delay-Line
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Electric field
50 meandering CPWtotal length s
xx
0,0 qxx
m2
12
eff
D
dG
Coplanar Waveguide (CPW)
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Some formulae about lossy CPW:
1m)()( CjGLjjj
m
F0 eff
LC ,
eff
r
C
LZ
0
00
11
m
12
12
eff
D
d
G
m
Np
2
m
rad
8
11
2
1
0
2 ln}Re{
Z
dDxx
Ls
sxx
L
Z
d
Zd
00
}Im{
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Where to put the nanostructures (QDs, QWs, QXs…..) on the sensors?
for CPW for SAW
You don’t need to connect the QDs one by one!
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What kind of information we can get?
Microwave adsorption , dynamics at microwave frequencies…
coming from:
intraband adsorption
cyclotron resonance
spin flipping, spin rotations, spin-spin interaction, spin-orbit interaction---for “spintronics”??
spinsE
Magnetic field
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Schematic of a homemade PLL system for microwave signals up to 18 GHz.
FM
The phase resolution is about 0.001 degree even under very low average input power (~-100dBm).
A special designed homodyne amplitude detection scheme also allows us to detect very small microwave adsorption.
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A homodyne amplitude detection scheme
0º 90º
Ref. Signal (LO)
Signal from the sample
90º hybrid
Power splitter
mixerTo PLL
To amplitude detection
~0
A home-made vector meter??
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Why pulsed?
1. Use low average power to prevent from heating
2. Use gated averaging technique to avoid direct EM interruption
3. Avoid the reflection and multiple reflection signals
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Signal Gating & Averaging:
RF/Microwave pulse train
3~4 ms set by a lock-in amp
~200 s set by a pulse generator
0.2~2 s set by a pulse shaping circuit
s1(t)
s1(t)
sampling delay set by a pulse generator
sampling gate set by a pulse generatorfed into the controlling node of a sample-and-hold circuit
s3(t)
time delays2(t) signal of mixer
Direct coupled EMReflected signals s4(t) signal after SH
Peak power about –30~-70dBm
fed into lock-in
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Typical data for CPW on 2DES:
0 2 4 6 8 10
0
2
4
6
8
10
Am
plitu
de (a
rb. u
nit)
200kHz=2 =1
f0=1.39GHz
B (T)
amplitude
f
(a) The pattern of the meandering coplanar waveguide. (b) The amplitude and the frequency deviation f vs magnetic field B are shown for f0=1.39GHz at T=0.3K.
(a) (b)
Re{xx}
Im{xx}
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0 2 4 6 8 10
f0=
T=0.3K
2.16G
=2 =1
1.74G
0.59G
0.96G
1.39G
500kHz
f
B (T)
2.92G
0 2 4 6 8 105
10
15
20
25
30
f0=
=2 =1
2.92G
2.16G
1.74G
1.39G
0.96G
0.59G
Am
plitu
de (
arb.
uni
t)
B (T)
More data:
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0.0 0.1 0.2 0.3 0.4 0.5 0.6-0.15
-0.10
-0.05
0.00
0.05
0.10
0.59GHz 0.96GHz 2.12GHz 2.92GHz
Im{
xx}
(e2 /h
)
Re{xx
} (e2/h)0.0 0.2 0.4 0.6 0.8
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
0.96GHz
Im{
xx}
(e2 /h
)
Re{xx
} (e2/h)
2.12GHz 2.92GHz
0.59GHz
Some plots for scaling analysis