Presented by

Petascale on Nanoscale:A Green’s Function Plane Wave Code for NanomaterialsORNL Electron Transport (OReTran) Code

Thomas C. SchulthessComputer Science and Mathematics Division

Center for Nanophase Materials Sciences

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Boron nitride nanotubes (predicted 1994,synthesized 1996) Pseudopotential

plane wave code

Successful predictions of new materials

Fe/MgO/Fe magnetic tunnel junction (predicted 2001at ORNL, synthesized 2004)

Layer-KKR and quantumtransport code

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For each energyFor each K-pointFor each energyFor each K-point

Integration of chargedensities over

K-pointsand energies

Integration of chargedensities over

K-pointsand energies

EndEnd

Conductanceand

nonequilibriumcharge density

Conductanceand

nonequilibriumcharge density

StartStartFlowchart of OReTran

ParametersParameters

InitializationInitialization

Fixed energy plane wave basisFixed energy plane wave basis

Block wave functions in the left and right leadsBlock wave functions in the left and right leads

Plane wave propagation matrix in the middle regionPlane wave propagation matrix in the middle region

Transmission and reflection matricesTransmission and reflection matrices

ConductanceConductance

Keldysh Green function andnonequilibrium charge densityKeldysh Green function and

nonequilibrium charge density

ReturnReturn

StartStart

InitializationInitialization

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x

z 2DES in x-z plane

Shaded (Rashba SO) region: Quantum dot array Patterned electrodes

Spin-polarized injection Different left and right

diffracted flux Transverse charge current

depends on the spin polarization of injection

Non-spin-polarized injection No transverse charge current Transverse spin current

Tunable spin Hall effect

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Spin-polarized injections

Wave densities for injected beam polarized along x or z direction

Diffraction patterns (charge lattices)

(x,z)(x,z) 2

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Transverse charge current

Period of QD array:b = 20 nm

Width of QD array:0 < a < 20 nm

Asymmetric diffraction transverse charge currents

δj depends on spin polarization of injected beam

0.0015

0.0010

0.0005

0.0000

- 0.0005

jj

0 5 10 15 20a (nm)

X

Z

Y

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Selective polarization flipping

Principal beam j0: Transmission P0: Polarization

Spin flipping for injection polarized along x or y

1.0

0.9

0.8

jj00

0 5 10 15 20a (nm)

X

Z

Y

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Magnetic Random Access Memory

Possible application

Different transverse charge current from differentspin-polarized injection: Spin current detector

Principal beamwith near-perfect transmission andhigh spin polarization

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Non-spin-polarized injection

Charge lattice (symmetric)

Spin lattice(anti-symmetric)

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Transverse spin current

No transverse charge current Transverse spin currents defined outside the SO region Real, dissipative, and detectable

Period of QD array:b = 20 nm

Width of QD array:0 < a < 20 nm

0

0.005

0.000

-0.005

-0.010

-0.015

jj

5 10 15 20a (nm)

xjz

yjz

zjz

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Contacts

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Gonzalo AlvarezOak Ridge National Laboratory(865) 241-5498Alvarezcampg@ornl.gov

Jun-Qiang LuOak Ridge National Laboratory(865) 574-1956luj1@ornl.gov

Xiaoguang ZhangOak Ridge National Laboratory(865) 241-0200zhangx@ornl.gov

Thomas SchulthessOak Ridge National Laboratory(865) 574-4344schulthesstc@ornl.gov