Spin-Hall field effect transistors
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Transcript of Spin-Hall field effect transistors
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SemiSpinNet
Research fueled by:
ASRC Workshop on Magnetic Materials and Nanostructures
Tokai, JapanJanuary 10th, 2012
Vivek Amin, JAIRO SINOVATexas A&M University
Institute of Physics ASCR
Hitachi CambridgeJoerg Wünderlich, Andrew Irvine, et al
Institute of Physics ASCRKamil Olejnik, Tomas
Jungwirth, Vít Novák, et al
University of Nottingham Tomas Jungwirth,
Richard Campion, et al.
Spin-Hall field effect transistors Spin-Hall field effect transistors
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2Nanoelectronics, spintronics, and materials control by spin-orbit coupling
I. Optical injection spin-Hall FET•Spin based FET: old and new paradigm in charge-spin transport•Theory expectations and modeling•Experimental results•Spin-current AND-gate
II. Spin Hall and non-local spin valve detection of electrically injected and manipulated spins:
•Spin amplifier and modulator•non-local spin accumulation measurements•Device and key issues•Modeling
III. Summary
spin-Hall field effect transistors spin-Hall field effect transistors
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Spin-orbit coupling interaction
(one of the few echoes of relativistic physics in the solid state)
This gives an effective interaction with the electron’s magnetic moment
Consequences•Effective quantization axis of the spin depends on the momentum of the electron. Band structure (group velocities, scattering rates, etc.) mixed strongly in multi-band systems
•If treated as scattering the electron gets asymmetrically scattered to the left or to the right depending on its “spin”
Classical explanation (in reality it is quantum mechanics + relativity )
• “Impurity” potential V(r) Producesan electric field
∇V
BBeffeff
pss
In the rest frame of an electronthe electric field generates and effective magnetic field
• Motion of an electron
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Problem: Rashba SO coupling in the Datta-Das SFET is used for manipulation of spin (precession) BUT it dephases the spin too quickly (DP mechanism).
From DD-FET to new paradigm using SO coupling
1) Can we use SO coupling to manipulate spin AND increase spin-coherence?
• Can we detect the spin in a non-destructive way electrically?
3) Can this effect be exploited to create a spin-FET logic device?
Use the persistent spin-Helix state or quasi-1D-spin channels and control of SO coupling strength (Bernevig et al 06, Weber et al 07, Wünderlich et al 09, Zarbo et al 10)
Use AHE to measure injected current polarization electrically (Wünderlich, et al Nature Physics. 09, PRL 04)
Spin-Hall AND-gate device (Wünderlich, Jungwirth, et al Science 2010)
DD-FET
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Spin-dynamics in 2D electron gas with Rashba and Dresselhauss SO coupling
a 2DEG is well described by the effective Hamiltonian:
Something interesting occurs when
[110]
[110]_
α = 0, β < 0 [110]
[110]_
ky [010]
kx [100]
α > 0, β = 0
1) Can we use SO coupling to manipulate spin AND increase spin-coherence?
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Local spin-polarization → calculation of AHE signal
Weak SO coupling regime → extrinsic skew-scattering term is dominant
Lower bound estimate
Spin-injection Hall effect: theoretical expectations
1) Can we use SO coupling to manipulate spin AND increase spin-coherence?
• Can we detect the spin in a non-destructive way electrically?
Use the persistent spin-Helix state or 1D-spin channelsand control of SO coupling strength
Use AHE to measure injected current polarization electrically
✓
✓
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Spin-injection Hall device measurements
trans. signal
σσooσσ++σσ-- σσoo
VL
SIHE ↔ Anomalous Hall
Wunderlich, Irvine, Sinova, Jungwirth, et al, Nature Physics 09
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T = 250K
Further experimental tests of the observed SIHE
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VH2
I
VbVH1
x
VH2
VbVH1
x
(a)
(b)
Spin injection Hall effect
Wunderlich, et al, Science 2010
SiHE
inverse SHE
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Spin-FET with two gates → logic AND function
Wunderlich et al., Science.‘10
SHE transistor AND gate
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11Nanoelectronics, spintronics, and materials control by spin-orbit coupling
I. Optical injection spin-helix and spin-Hall FET•Spin based FET: old and new paradigm in charge-spin transport•Theory expectations and modeling•Experimental results•Spin-current AND-gate
II. Spin Hall and non-local spin valve detection of electrically injected and manipulated spins:
•Spin amplifier and modulator•non-local spin accumulation measurements•Device and key issues•Modeling
III. Summary
spin-Hall field effect transistors spin-Hall field effect transistors
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+
–
ID
+
–
Electrical injection, manipulation, and detection of spins in semiconductors
Electrical injection spin-amplifier (modulator) in Fe/GaAs(3D)
FM FM
FM FM
injection from a FM detection of spin current by iSHE
detection of spin polarization by FM
electrical manipulation of the spin profile by a drift current
Huang et al 07
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Experimental device set-up
IB ID
Fe FeAu Au
VSH
VNL
n-GaAs
Note: ID reminiscent of base current in the bipolar transistor amplifier IB ↔ emitter current detected spin polarization (current) ↔ collector current
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Electrical non-local spin valve detection by FM and by iSHE
Electrical injection of a diffusive spin current from FM into a non-magnetic metal
Valenzuela, S. O. & Tinkham, M, Nature‘06
iSHE NL spin detection
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Valenzuela, S. O. & Tinkham, M, Nature‘06
xy
zBz
Electrical non-local spin valve detection by FM and by iSHE
Electrical injection of a diffusive spin current from FM into a non-magnetic metal
iSHENL spin detection
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high-resitive semiconducor
low-resistive FM metal
Lou et al. Nature Phys.’07, Ciorga et al. PRB 09, Awo-Affouda et al. APL 09, Salis et al. PRB 09
Fe/n-GaAs Schottky tunnel contacts
very high-resitivespin-dependent tunnel contact↓
Electrical non-local spin valve detection by FM and by iSHE
Electrical injection of a diffusive spin current from FM into a non-magnetic semiconductors
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high-resitive semiconducor
low-resistive FM metal
Lou et al. Nature Phys.’07, Ciorga et al. PRB 09, Awo-Affouda et al. APL 09, Salis et al. PRB 09
Fe/n-GaAs Schottky tunnel contacts
... and by iSHE ?
very high-resitivespin-dependent tunnel contact↓
Electrical non-local spin valve detection by FM and by iSHE
Electrical injection of a diffusive spin current from FM into a non-magnetic semiconductors
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n-GaAs
FeAl
xy
z
xy
zBz
Key is to experimentally remove the strong ordinary Hall effect in SCs
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n-GaAs
Al
BX
x
y
z
x
y
z
Fe
Key is to experimentally remove the strong ordinary Hall effect in SCs
Hanle + iSHE
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Baniso ≈ 200 mT >> BHanle ≈ 50 mT
BX
x
y
z
x
Epitaxial 2 nm Fe on n-GaAs grown in one MBE → large [110]/[1-10] in-plane anisotropy
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Plus we know when each Fe electrode switches for a given φB
Bx
y
z
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(ordinary Hall)
BX
x
y
z
x
iSHE
Hanle iSHE
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Easy-axis switching NL spin-valve
Hanle iSHEHard-axis Hanle NL spin-valve
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Nuclear (Overhauser) field:
xy
z
Bz
BX
x
y
z
Bz,aniso ≈ 2 T
Bx,aniso ≈ 200 mT
Hanle curves affected by nuclear fields
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Hanle curves affected by nuclear fields
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iSHE reverses sign upon reversing spin-current
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Electrical spin modulator
Bx=0
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Drift-diffusion equations
1. sy continuous at x=0
2. independent of vd(x)
Bx=0
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Drift velocities
Diffusion constant
Spin lifetime
Bx=0
Overall magnitude ( source term )
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TheoryExperiment
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Spin current
Hall sensitivity function for a finite-size cross
iSHE voltage
(~ skew scattering Hall angle in GaAs)
SHE analysis from calibrated spin-current
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TheoryExperiment
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Experiment Theory
skew scattering Hall angle in GaAs:
Theory - experiment comparison
Summary of theory
•DD-equation with non-constant vd analysis•Spin-lifetime from out of plane Hanle•Fit of DD to NL yields polarization at injection FM electrode•Use this injected spin-current estimate to calculate predicted spin Hall angle (because of geometry one needs to calculate the sensitivity function for the Hall cross bar).
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Summary of spin-injection Hall FET
Basic studies of spin-charge dynamics and Hall effect in non-magnetic systems with SO coupling Spin-photovoltaic cell: solid state polarimeter on a semiconductor chip requiring no magnetic elements, external magnetic field, or bias
SIHE can be tuned electrically by external gate (e.g. Fe/Ga(Mn)As structures)
Spin amplifier-modulator based on drift current iSHE and NL in semiconductor device
Strongest theory-experiment comparison to date in SC
optical-spin-injection Hall FET
all electrical Hall FET