Spin-Hall field effect transistors

transcript

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

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

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

BBeffeff

In the rest frame of an electronthe electric field generates and effective magnetic field

• Motion of an electron

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

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]_

α = 0, β < 0 [110]

[110]_

ky [010]

kx [100]

α > 0, β = 0

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

• 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

Spin-injection Hall device measurements

trans. signal

σσooσσ++σσ-- σσoo

SIHE ↔ Anomalous Hall

Wunderlich, Irvine, Sinova, Jungwirth, et al, Nature Physics 09

T = 250K

Further experimental tests of the observed SIHE

Spin injection Hall effect

Wunderlich, et al, Science 2010

inverse SHE

Spin-FET with two gates → logic AND function

Wunderlich et al., Science.‘10

SHE transistor AND gate

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

Electrical injection, manipulation, and detection of spins in semiconductors

Electrical injection spin-amplifier (modulator) in Fe/GaAs(3D)

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

Experimental device set-up

Fe FeAu Au

n-GaAs

Note: ID reminiscent of base current in the bipolar transistor amplifier IB ↔ emitter current detected spin polarization (current) ↔ collector current

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

Valenzuela, S. O. & Tinkham, M, Nature‘06

Electrical injection of a diffusive spin current from FM into a non-magnetic metal

iSHENL spin detection

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 injection of a diffusive spin current from FM into a non-magnetic semiconductors

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 injection of a diffusive spin current from FM into a non-magnetic semiconductors

n-GaAs

Key is to experimentally remove the strong ordinary Hall effect in SCs

n-GaAs

Key is to experimentally remove the strong ordinary Hall effect in SCs

Hanle + iSHE

Baniso ≈ 200 mT >> BHanle ≈ 50 mT

Epitaxial 2 nm Fe on n-GaAs grown in one MBE → large [110]/[1-10] in-plane anisotropy

Plus we know when each Fe electrode switches for a given φB

(ordinary Hall)

Hanle iSHE

Easy-axis switching NL spin-valve

Hanle iSHEHard-axis Hanle NL spin-valve

Nuclear (Overhauser) field:

Bz,aniso ≈ 2 T

Bx,aniso ≈ 200 mT

Hanle curves affected by nuclear fields

iSHE reverses sign upon reversing spin-current

Electrical spin modulator

Drift-diffusion equations

1. sy continuous at x=0

2. independent of vd(x)

Drift velocities

Diffusion constant

Spin lifetime

Overall magnitude ( source term )

TheoryExperiment

Spin current

Hall sensitivity function for a finite-size cross

iSHE voltage

(~ skew scattering Hall angle in GaAs)

SHE analysis from calibrated spin-current

TheoryExperiment

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).

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

Spin-Hall field effect transistors

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