Silvano De Franceschi Laboratorio Nazionale TASC INFM-CNR, Trieste, Italy http://www.tasc.infm.it/~defranceschis/SilvanoHP.htm Nanowire growth and properties Integration with Si technology Manipulation and NEMS Single electron transport Gate-controlled proximity supercurrent Outli ne
Outline. Nanowire growth and properties Integration with Si technology Manipulation and NEMS Single electron transport Gate-controlled proximity supercurrent. Quantum transport in semiconductor nanowires. Silvano De Franceschi. Laboratorio Nazionale TASC INFM-CNR, Trieste, Italy. - PowerPoint PPT Presentation
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Silvano De Franceschi
Laboratorio Nazionale TASC INFM-CNR, Trieste, Italy
• Differential conductance (black: low, white: high);• Many diamonds visible. Not so regular, but very stable and reproducible.• Single & Multiple(probably two)-island behavior
Typical island size:~100 nm
L
-100 -90 -80 -70 -60 -50 -40 -30
0.00
0.01
0.02
0.03
Co
nd
ucta
nce
(e
2 /h)
Gate voltage (mV)
B = 31 mT B = 0.5 T
V (V
)
Vg (mV) Vg (mV)
gBBg = 1.5 ± 0.2
InP-nanowire quantum dot: Zeeman spin splitting
E
N N+1
Tunable Quantum Dots
top gates
source
drain
Side gates
Few-electron quantum dots in InAs/InP nanowires
Björk et al., Nano Lett. 4, 1621 (2004)InAs QD
InP barriers
S SN (1-D or 0-D)
Kasumov et al, Science 284 (’99)Morpurgo et al., Science 286 (’99)Buitelaar et al., PRL 89 (’02); PRL 91 (‘03)Jarillo-Herrero et al. (unpublished)
Superconductor Nanowire Superconductor
For T < 1.2 K
Only a few experiments done on similar hybrid systems based on carbon nanotubes:
Superconducting contacts => Proximity effect
Low contact resistance => no Coulomb blockade
InAs nanowire devices
500 nm500 nm
Ti(10 nm)/Al(120 nm)
Lsd = 60 – 500 nm
I+
I-
V+V-
I+
I-
V+V-
Vgate
SiO2
Si (p+)
4-point contacts:InAs [100]
Lsd
W
sour
ce
drai
n
Device resistances: 0.4 – 4 K
-150 -100 -50 0 50 100 150
-40
-20
0
20
40
IR
IC
V
(V
)
I (nA)
Supercurrent in InAs nanowires
T = 40 mK
IC = 136 nARN = 417 ICRN = 60 V ~ 0/e
Hysteretic behavior due to strong capacitive coupling between source and drain
0 4100
101
102
I C(n
A)
RN(k)
(90 % device yield!)
Enhanced conductance for 20<V<20
High contact transparency (T~75%)
0.0 0.4
0
1
100 mT
0 mT
I (A
)V (mV)
B=0
20/e
Multiple Andreev reflection
0.0 0.5
1.0
1.5
RNdI
/dV
V2
V3
V1
V (mV)
0.0 0.40
1
100 mT
0 mT
I (A
)V (mV)
-2 -1 0 1 2
1.0
1.5
RNdI
/dV
V/20
From 3 different devices:
Peaks at Vn=20/ne:V1=20/eV2= 20/2eV3= 20/3e
Normal Super
N S
T < Tc
And
reev
ref
lect
ion
in a
S-N
junc
tion
Field-effect control of the supercurrent
Supercurrent fluctuations correlate with normal-state universal conductance fluctations
-2 -1 0 1 2
-10
0
10
-71 V -61 V -50 V -40 V -30 V -20 V -10 V 0 V
V
(V
)
I (nA)
Vgate
-70 -60 -50 -40 -30 -20 -10 0 10 20 30
-2
-1
0
1
2
Vg (V)
I (n
A)
0 5 10 15 20
dV/dI (kOhm)
#S1_B (Iv_8_14 (1026; 1027)
246810
GN (e
2/h)
-70 -60 -50 -40 -30 -20 -10 0 10 20 30
-2
-1
0
1
2
Vg (V)
I (n
A)
0 5 10 15 20
dV/dI (kOhm)
#S1_B (Iv_8_14 (1026; 1027)
246810
GN (e
2/h)
-70 0-2
0
2I (
nA)
Vg (V)0 30 k
2
4
GN (2
e2/h
)
Electron transport through the nanowire is diffusive and phase coherent
=> mesoscopic Josephson junctions
First Josephson Field Effect Transistors:
Takayanagi et al., PRL (1985). Kleinsasser et al., Appl. Phys. Lett. (1989). Nguyen et al., Appl. Phys. Lett. (1990).
-40 0 40 80 120-60
-30
0
30
60
-4
4
N = 0
-3
-2
3
2
1
V
(V
)
I (nA)
w/o rf rf = 4.836 GHz
No.6B
-1
V=10 V
V= (/2e)rf
= 2.068 V for 1 GHz
“Quantized voltage steps depending on RF frequency” 0 5 10
0
10
20 No.6B 2.068 uV/GHz
V (V
)
rf (GHz)
AC Josephson effect: Rf irradiation => Shapiro steps
Shapiro steps: rf-power dependence
200 400
-60
-40
-20
0
20
40
60300 600 900
-80
-60
-40
-20
0
20
40
60
80
I (n
A)
Irf (arb.)
0 001 1 1
-1 -1 -1
23
45
67
8
-2-3
-4-5
-6-7-8
0
1
2
3
4
5
-1
-2
-3
-4
-5
rf = 2 GHz rf = 4 GHz rf = 5 GHz
IN ~ N-th order Bessel function with IC,fit = 34 nA > IC,exp = 26 nA
IC
IN=1
IN=2
IN=3
IN=4
(a) (b) (c)
0 2 4 6 80
5
10
15
20
25
In
=4 (
nA
)
Iac
(arb.) Bessel
0
5
10
15
20
25
In
=3 (
nA
)
0
5
10
15
20
25
In
=2 (
nA
)
n2
0
5
10
15
20
25
In
=1 (
nA
)
0
5
10
15
20
25
Ic (n
A)
Sam. #6B, rf = 5 GHz
Ic,fit
= 34 nA
Gate-controlled SQUID
Jorden van DamFloris ZwanenburgL. GurevichYong-Joo DohLeo Kouwenhoven
Erik BakkersAarnoud RoestLou-Fe Feiner
Philips Eindhoven:
Epitaxial III-V nanowires on Ge [Nature Materials 3, 769 (2004)]Nanowire SET [Appl. Phys. Lett. 83, 344 (2003)] Nanowire JOFET [Science 309, 272 (2005)] Nanowire SQUID [unpublished]