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Thomas C. Schulthess Computer Science and Mathematics DivisionPowerPoint Presentation

Thomas C. Schulthess Computer Science and Mathematics Division

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

Thomas C. Schulthess

Computer Science and Mathematics Division

Center for Nanophase Materials Sciences

Successful predictions of new materials

- Fe/MgO/Fe magnetic tunnel junction (predicted 2001at ORNL, synthesized 2004)
- Layer-KKR and quantumtransport code

- Boron nitride nanotubes (predicted 1994,synthesized 1996)
- Pseudopotentialplane wave code

Flowchart of OReTran

Start

Start

Initialization

Initialization

Fixed energy plane wave basis

Parameters

Block wave functions in the left and right leads

For each energy

For each K-point

Conductanceand nonequilibriumcharge density

Plane wave propagation matrix in the middle region

Transmission and reflection matrices

Integration of chargedensities overK-pointsand energies

Conductance

Keldysh Green function andnonequilibrium charge density

End

Return

x

Tunable spin Hall effect- 2DES in x-z plane
- Shaded (Rashba SO) region:
- Quantum dot array
- Patterned electrodes

- Spin-polarized injection
- Different left and rightdiffracted flux
- Transverse charge currentdepends on the spin polarization of injection

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

Spin-polarized injections

- Wave densities for injected beam polarized along x or z direction
- Diffraction patterns (charge lattices)

Y

Z

Transverse charge current0.0015

- Period of QD array:b = 20 nm
- Width of QD array:0 < a < 20 nm

0.0010

0.0005

j

0.0000

- 0.0005

0

5

10

15

20

a (nm)

- Asymmetric diffraction transverse charge currents
- δj depends on spin polarization of injected beam

Y

Z

Selective polarization flipping1.0

- Principal beam
- j0: Transmission
- P0: Polarization

- Spin flipping for injection polarized along x or y

0.9

j0

0.8

0

5

10

15

20

a (nm)

Possible application

- Different transverse charge current from differentspin-polarized injection:Spin current detector
- Principal beamwith near-perfect transmission andhigh spin polarization

Transverse spin current

0.005

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

0.000

- Period of QD array:b = 20 nm
- Width of QD array:0 < a < 20 nm

-0.005

xjz

j

yjz

-0.010

zjz

-0.015

5

10

15

20

0

a (nm)

Contacts

Thomas Schulthess

Oak Ridge National Laboratory

(865) 574-4344

Gonzalo Alvarez

Oak Ridge National Laboratory

(865) 241-5498

Jun-Qiang Lu

Oak Ridge National Laboratory

(865) 574-1956

Xiaoguang Zhang

Oak Ridge National Laboratory

(865) 241-0200

11 Schulthess_Dynamics_0611

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