Download Cooperative Spintronics Research

Collective Effects
Kang L. Wang
Raytheon Distinguished Professor of Physical Electronics
Device research Laboratory
Center on Functional Engineered NanoArchitectonics -- FENA
(www.fena.org)
Western Institute of Nanoelectronics – WIN
(www.win-nano.org)
California NanoSystems Institute – CNSI
(www.cnsi.ucla.edu)
University of California - Los Angeles
E-mail: [email protected])
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Outline
 Introduction

Interaction in the space and the Order
Parameter
 Collective effects and state variables
 Variability issues of spintronics versus
nanoelectronics
 Examples:
 Spin
wave bus
 MQCA
 SPIN FET
 Molecules and atoms
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Summary
2
Charge State Variable (RT)
Conventional Electronics employs indept
electron entity and Coulomb interaction
C  1/r
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 As the size of the
devices goes down, the
Coulomb (electrostatic)
Capacitance energy
arises.
 Leading to the increase
of the energy per one
electron and thus to
high variability as
quantum fluctuations
become important
E  e /C
Vdd
2
u-nm
r
Order Parameter
The solution:
To switch to
interactions other than
Coulomb
3
Corrections for Coulomb Energy
Whatever the new interaction will be it is going
to the some part of the ELECTRODYNAMIC
interaction:
ElectroDynamic Interaction = Coulomb + Corrections
Many-body or Quantum
Single electron level
dynamic
static
(relativistic  v/c) (multipole, short-ranged  1/r n,n>2)
Too weak to work with
Dynamic: of relativistic origin
including spins, magnetic, multiferroics
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E> KT
Effective interactions
in many-electron
collective variables
Static: Multi-pole, short ranged
~ 1/rn, n>2
Ferroelectric
Big Molecules (collective variables)
4
Many-electron collective variables for
information processing
Examples of the order parameters and collective variables
Ferromagnetic
r
Ferroelectric
e
M
Magnetization
order parameter
e
r
D
Collective variable
representing the state of
many-electron system (e.g.,
position)
r
M
r
D
Dipole moment order parameter
(bose-condensation of plasmons)
Molecules
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Miltiferroic
Both previous order parameters
These we can call a first level
collective variables, they are
actually fields
r r inr space
r
M(x),D(x)
Excitations of these can be
called a second level
collective variables
5
Excitations of the order parameters as the second
level collective variables
Domain walls in
ferromagnets
(1 wall)
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Fixed
layer
on
Goldstone
excitations of the
order parameter: for
example spin waves:
off
on
oxide
layer
Free layer
(no wall)
Fixed
layer
off
oxide
layer
Free layer
MTJ memory unit can be
view as a domain-wall trap
Topological
excitations of the
order parameters:
for example
ferromagnetic
vortices
Is it possible to use
Ferroelectric or even
MultiFerroic , Domain walls,
Topological excitations,
Goldstones?
Are they advantageous in any
way ?
6
Variability: Electronics vs Spintronics
Electronics
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Spintronics
The Same Principle for elemental Electrics and
Spintronics circuit units (FET and spin-FET)
7
Variability Issues
 Electronics
 Spintronics
V /V   C / C
CN
1/ 3
a
Total range spin vector = 2S+1
q/6
 2.4 10
20
N
1/ 3
a
Farads
( bulk N a ) 1
 /   1/(2S  1) 
2
where  bulk is the Bohr magneton
per atom, and for Ni is 0.33
V / V  N
1
stair
6
 1/ 3 eV
Na
2.8
 /    S / S 
Na
Thermal fluctuations give Gaussians:
8
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6
TN  1/ 3 (eV )
Na
2.8
TS 
(eV )
Na
8
Variability
Charge
Spin
 N a  N  1/ C  (6 eV / To )
3
~ 10
or a linear length of 77 nm
7
 N a S  2.8 eV / To ~ 10
or a linear size of 1.6 nm
• High enough
energy
• Collective
particles
Room Temperature.
Quantum fluctuations of the projection of the Spin
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2
Ovchinnikov and Wang, APL 2008
10
Spintronics for low power – Spin as a
state variable
E  kBT ln r
For Single Spin
e
B 
2me
1
E
 exp( 
)
r
k BT
E  g B B
For N Spins
E  2.B  2N B B
11
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E=2 B B = 1.157×10-4 eV at 1 T)
Bmin155 Tesla –
Not practical!
E  NkBT ln 2 if independently
Single electron or collective variables
should be used to satisfy thermal stability
and power dissipation requirements
E ~ kBT ln r if collectively
E ~ kBT ln r per variable
Datta, APL 90, 093503(2007)
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Summary Comparison of Electronic, Spin
and Optical State Computing
Independent electrons
Lower bound
(Impractical Limit)
Mechanism
Energy
Size
Electronic
3kBT
1 nm
Practical limit ~3-5 nm
Spin
70kBT
7 nm
Practical limit >20 nm
Optical
3600kBT
20 nm
Practical limit >90 nm
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Victor Zhirnov
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Summary Comparison of Electronic, Spin
and Optical State Computing
Correlated electrons
Mechanism
Lower bound
(Impractical Limit)
Energy
Size
Electronic
3kBT
1 nm
Practical limit~20~70 nm
Spin
3kBT
2 nm
Practical limit ~2~7 nm
Optical
3600kBT
20 nm
Practical limit >90 nm
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Spin Logic Devices
Phase modulation/Amplification/
Superposition
Spin Waves
Magnetic
Cellular
Automata
I3
output
I1
I2
Sugahara- Tanaka
Spin FET
3-terminal
RAP
Spin Valves/Spin
Torque
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Paralle
l
AntiParalle
l
0
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Spin Wave Bus -- Spin-Based Logic Device
and transfer of information (Phasetronics)
Three terminal device
(three MOS with a common
ferromagnetic film)
Two inputs – One output
The input is provided by a
Source -Drain current pulse ISD
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The output is the inductive
voltage between two nearest
source ( or drain) contacts VSS
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Experiment – Spin wave Propagation
Signal/Pulse
Generator
Oscilloscope
50 GHz
circulator
100 nm NiFe
ACPS line
ACPS line
Z
X
50
m
Y
SiO2
Magnetic Film
Time resolved inductive voltage
measured
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2
m nm
Quartz or Semiconductor
Substrate
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Experimental Data – SW
transport in CoFe film
Phase shift (Degree)
Amplitude changes (dB)
6.0
6.0
5.5
5.5
5.0
5.0
Frequency (GHz)
3dB
4.0
2dB
3.5
1dB
3.0
0dB
-1dB
2.5
-2dB
2.0
-3dB
1.5
-4dB
Frequnecy (GHz)
4dB
4.5
4.5
45Deg
4.0
35Deg
25Deg
3.5
15Deg
3.0
5Deg
2.5
-5Deg
-15Deg
2.0
-25Deg
1.5
-35Deg
1.0
1.0
0.5
0.5
0
0
50
100
150
200
250
300
50
100
150
200
250
300
External magnetic field (Oe)
External magnetic field (Oe)
 Prominent modulation by weak (10  50 Gauss) magnetic field
M. Bao, J-Y Lee, A Khitun, K. L Wang, D. W. Lee and S. Wang, 3-D mapping of spin
wave propagation in CoFe thin film, (2007).
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General Concept and Some Results
6.0
5.5
5.0
4dB
4.5
Frequency (GHz)
 Experimental data on amplitude and phase
modulation for the structure with 100nm CoFe
film in the frequency range
(0.5  6 GHz) and magnetic field range (0 
350G)
 Prominent power (8dB/20G) and phase
modulation ( 60Deg/10G) in the specific
frequency regions
Amplitude changes (dB)
3dB
4.0
2dB
3.5
1dB
3.0
0dB
-1dB
2.5
-2dB
2.0
-3dB
1.5
-4dB
1.0
0.5
0
50
100
150
200
250
External magnetic field (Oe)
“AND”, “OR”, “NOT” gates
Maj
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300
Prototype Three-Terminal Device




Logic state - spin wave phase
Spin wave interferometer
Phase control by the direction of
current in the excitation loop
Only two phases 0 and 
detection
Input 1
Input 2
Out-of-Phase
In Phase: Amplification
Out of Phase: Cancellation
Output Voltage (mV)
In-Phase
12 In-phase
Out of phase
Frequency = 3GHz
10
8
6
4
2
0
0
100 200 300 400 500 600 700 800
Magnetic Field (Oe)
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A. Khitun, M. Bao, Y. Wu, J-Y Kim, A. Hong, A. Jacob, K. Galatsis, and K. L. Wang, Logic Devices with Spin Wave Buses – an
Approach to Scalable Magneto-Electric Circuitry, Proceeding of MRS, (in press), 2008
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Mitigating eddy current losses in
nanoscale devices
CoFe; 100 nm
Ferrite
(Fe3O4)
Insulating film
2, 4,
or 8 m
100
"Insulator"
10
25
Eddy current losses
20
1
Frequency, GHz
30
35
30
0.0
0.5
Fig. (1)
1.0
1.5
2.0
0.1
k, waves/micron
2 m
10
25
4 m
1
20
15
15
Dispersion
0.0
Wide film
8 m
0.5
1.0
1.5
2.0
k, waves/micron
Decay length, microns
100
Dispersion
Decay length, microns
Frequency, GHz
35
0.1
Fig. (2)
CoFe; 100 nm
0.1 T
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Continuous metallic
Eddy current losses severely damp
spin waves in a metallic film.
Continuous metallic
Eddy current loss can be
reduced by laminations.
Jim Allen – UCSB
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Prototype Device by Kostylev et al:
Logic state - spin wave amplitude
 Spin wave interferometer
 Phase modulation by magnetic field
 Gradual phase shift control up to 2.5

I, A
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Interferometer output signal amplitude, dB
/
2D Graph 2
f0
-5
-10
U
-15
-20
-25
-30
=0.8
=0
-35
Umin
-40
7.095
7.100
7.105
7.110
7.115
7.120
Spin wave frequency, GHz
Kostylev, M.P., et al., Spin-wave logical gates. APL, 2005. 87(15): p. 153501-1-3.
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7.125
Follow-up work by T. Schneider et al.
 The
same device structure as for the prototype (Kostylev et al.)
 Logic state - spin wave amplitude
 Phase modulation by magnetic field (Input current 1200mA
 XNOR, NAND logic gates demonstrated
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T. Schneider, A.A. Serga, B. Leven, B. Hillebrands, R.L. Stamps and M.P. Kostylev, Realization of spin-wave logic gates, APL, 92, 0022505, 2008
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Speed of Operation
 Internal delay time = propagation distance/group
velocity
Propagation distance: ~ (submicron)
Group velocity: gr= d/dk (~ 107 cm/s )
Experimental Data:
Delay time ~ 10-100 ps
100nm CoFe film, RT
Propagation distance: 2
Group velocity: ~105 m/s or 107cm/s
 Current device: 1 ns
 Ultimate limit: <10 ps
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Oscilloscope Output (mV)
 The fundamental limit for device
operation speed – limited spin
wave group velocity.
 operation speed by the scaling
down the signal propagation
distance (submicron)
15
9
6
3
0
-3
-6
-9
-12
-15
0.0
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Subtracted H=0 from H=50 Oe
0.5
1.0
1.5
Time (ns)
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2.0
Numerical modeling: Multifunctional
MagnetoElectric Cell
Landau-Lifshitz-Gilbert formalism

 
dm
  

m  H eff  m  H eff
dt
1 2


m - the unit magnetization vector
Ms - the saturation magnetization
 - the gyro-magnetic ratio
 - the phenomenological Gilbert coefficient
M
V

2 A 2  2K    
H eff   2  
 m
(m  e )e  H pulse
Ms
Ms
A - the exchange constant
K - the uniaxial anisotropy constant
e - the unit vector along with the uniaxial direction
Hpulse - the pulse field
Sang-Koog Kim, Sung-Chul Shin, and Kwangsoo No
Seoul National University, IEEE TRANSACTIONS ON
MAGNETICS, VOL. 40, NO. 4, JULY 2004
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Spin Wave Modulation by Electric Field
R. Ramesh (Berkeley)
 Modulation via the exchange bias coupling
in FM/MF structure
S. Wang (Stanford)
K. Wang (UCLA)
Work Integrated by Ajey P. Jacob (Intel)
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Magnetic Nanofabric: Spin Wave multibit
processor
ACPS Line
(input f1,f2,f3,…fn)
Silicon Oxide
Modulator
fn
ME Cell
ACPS Line
(output f1,f2,f3,…fn)
fn
Silicon Oxide
Piezoelectric
Ferromagnetic Film
Silicon Substrate
Input
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Output
Equivalent circuit
(f1,f2,f3,…fn)
VC (f1)
VC (f2)


(f1,f2,f3,…fn)
VC (fn)
…

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Magnetic Nanofabrics:- Spin Wave device’s building
blocks- A. Khitun, M. Bao and K. L. Wang (UCLA)
Basic Element /Symbol
Structure Schematics

H ext
Voltage Input
Converter
Voltage-to-Spin Wave
Insulator (e.g. SiO2)
Ferromagnetic Film (e.g. CoFe)
Spin Wave Output
Semiconductor Substrate (e.g. Si)

Inductive Voltage Output
t = -
Spin Wave-to- Voltage
Insulator (e.g. SiO2)
(a)
Spin Waves Input
(1)
(2)
Semiconductor Substrate (e.g. Si)
1 m
Splitter/Combiner
Output A
50 nm
Input
Output B
Input A
Output
(b)
Input B
Conducting Wire
Spin Wave Modulator

Im

Hm
Insulator
Ferromagnetic Film
Semiconductor Substrate
(c)
VG
Magnetoelectric Cell (ME)
(e.g. Piezoelectric-Piezomagnetic)
Metal gate
Ferroelectric (e.g. PZT)
Ferromagnetic Film (e.g. CoFe, NiFe)
(d)
PAGE
5/
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27
Silicon Substrate
27
SW Logic Efficiency Estimates
Energy per bit
Energy to excite spin wave
a) External magnetic field (e.g. coil)
b) Internal excitation (e.g. spin torque)
Number of functions without
restoration (amplification)
a)
Physical Parameter
Estimated Range
Spin wave energy
1kT – 100kT
E SW   0 MH extVSW
(Hext ~ 100Oe, VSW: 0.1um2 - 0.01um2)
Energy to create a magnetic field
102kT – 104kT
Eloop  I  Z   ext
2
ext
 M 

 
 Ms 
2
 2h  Z


    ext
2
Spin wave coherence length /wavelength
L/
(M/M ~0.01, ~107 rad/s/Oe, Z~50Ohm,  ~ 10-12s)
h: 1um – 10nm
Ref.1
100-1000
(L ~ 50um@RT) : 100nm-10nm
102kT-105kT
Signal restoration energy
Electromagnetic coupling
f CV 2
Ediss 
Eii   ij H jj
Q 2
 - magnetoelectric coupling
range from 10 to 1000 mV/(cm Oe) Ref.2
Signal propagation speed
Spin wave group velocity
106 cm/s - 107cm/s
Time delay

vg 
k
(function of film thickness)
Propagation length/Spin wave velocity
0.05ns-1ns
d / vg
d range from 1um to 100nm
Scaling factor and Defect
Tolerance
Spin wavelength
Operation frequency
Spin wave frequency


10nm - 100nm
(insensitive to defects with size << )
1GHz - 200GHz (NiFe, CoFe)
Ref.3,4
(depends on the material structure)
1) Khitun A., Nikonov D.E., Bao M., Galatsis K., and Wang K.L., Feasibility study of logic circuits with spin wave bus. Nanotechnology 18, p. 465202, 2007.
2) Eerenstein, W., N.D. Mathur, and J.F. Scott, Multiferroic and magnetoelectric materials. Nature, 2006. 442(17): p. 759-65.
3) Covington, M., T.M. Crawford, and G.J. Parker, Time-resolved measurement of propagating spin waves in ferromagnetic thin films. Physical Review Letters, 002. 89(23): p. 2372021-4.
4) Vasiliev S.V., Kruglyak V.V.,Sokolovskii M.L., and Kuchko A.N., Spin wave interferometer employing a local nonuniformity of the effective magnetic field, JOURNAL
28 OF APPLIED
PHYSICS 101, p. 113919 (2007).
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Spin Wave Logic Devices
Experimentally demonstrated devices:
M.P. Kostylev, A.A. Serga, T. Schneider, B. Leven, B. Hillebrands, Spin-wave logical
gates. APL, 87(15): p. 153501-1-3, 2005.
T. Schneider, A.A. Serga, B. Leven, B. Hillebrands, R.L. Stamps and M.P. Kostylev,
Realization of spin-wave logic gates, APL, 92, 0022505, 2008
A. Khitun, M. Bao, Y. Wu, J-Y Kim, A. Hong, A. Jacob, K. Galatsis, and K. L. Wang,
Logic Devices with Spin Wave Buses – an Approach to Scalable Magneto-Electric
Circuitry, Proceeding of MRS, (in press), 2008
Ferromagnetic resonance controlled by electric field:
A.A. Semenov, S.F. Karmanenko, V.E. Demidov, B.A. Kalinikos, S. Grinivasan, A.N.
Slavin, J.V. Mantese, Ferrite-ferroelectric layered structures for electrically and
magnetically tunable microwave resonators. APL 88, 033503, 2006.
Spin wave modulation using multiferroics:
None
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Magnetic Logic - Cellular Automata
NAND gates form the building
blocks for circuits inside your
computer
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Logic Gates using MQCA
=
Current state-of-the-art: the majority
logic gate.
Imre et al, Science 311, 205 (2006)
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Instability of bits
0° is unstable
Energy (normalized) vs. θ
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32
Vertical Lines
The
TheProblem
Solution– –stray
Add fields
stabilizing
causebits
vertical
to leftbits
andtoright
flip first
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The B-gate (NAND function)
00
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10
01
11
D. Carlton, UCB
34
these gates can be linked together to do logic...
=
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D. Carlton, UCB
35
Nano magnet Switching speed
Direct observation of spin transfer switching by
x-ray microscopy.
c
a c
b
b
a) 0 ns
• 20 nm CoPt free layer
• 5 nm Cu as a tunneling
layer
• Fe as Fixed layer
b) 0.15
ns
d) 8.6 ns
e) 9.0 ns
f) 9.6 ns
g) 12.0 ns
h) 12.2
ns
i) 13.2 ns
Y. Acremann et al., PRL 96, 217202/1-4 (2006)
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dd f
ee
gg h i
f 0.6
h
c)
ns
i
Joachim Stöhr – SLAC
with Yves Acremann
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Spin FET
Field Effect in DMS Confirmed
Al
Al2O3
MnGe on n-type Ge substrate
2 Field-Effect
Moment (10-5emu)
MnGe
Ge
Al
1
0
-3V
-6V
-12V
-30V
0V
30V
-1
-2
-3000 -2000 -1000
0
1000
2000
3000
Field (Oe)
Schematic Spin gain FET
structure with a MnGe/SiGe
quantum well.
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Transistor
with
Memory
JingJing Chen and KL Wang et al., App. Phys. Letts. 90, 012501 2007
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Molecular Building Blocks
Physical Molecular Change
Molecular Motion
 store
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Rotational
Conformation
 2 2m

1
~
 exp 
(a Eb ) 
Ptun


MEMORY applications
Phase Change
tsw  L  L m
v
2 Eb
LOGIC applications
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Molecular Rotation - metallacarboranes
Metal carborane molecules
“electronic switching”
Atomic Scale: 90 rotation Cu(II)   Cu(I)
Tetrahedral
Rotor
“ON”
Square
planar
“OFF”
Stator
-3
Current density (A/cm2)
1.0x10
-4
5.0x10-4
Cu(I)(dmp)(phen-Si)PF6
Cu(I)(dmp)(bisp-Si)PF6
0.0
-4
-5.0x10-4
5.2eV
LUMO
-3
-1.0x10-3
-3
-1.5x10-3
-10
4.6eV
4.1eV
EF
-5
0
Voltage (V)
5
10
Ec
Metal
I-V characteristics
• Negative differential resistance due to
tunneling through molecular rotor
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• Hysteresis due to rotation
EF
Ev
HOMO
P+ Si
39
Acknowledgments





V Zhirnov and R Cavin
A Jacob, J Allen, A Khitun, I Ovchinnikov,
M Bao
H Ohno, Tanaka, and K Ando
All the FENA, WIN & CNSI participants
All students, postdoctoral fellows, Faculty
and visitors as well as collaborators
around the world
Support: DARPA, SRC, NSF, Marco, NERC, ARO,
AFOSR, ONR, and many industrial companies
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