Petascale on Nanoscale A Greens Function Plane Wave
- Slides: 11
Petascale on Nanoscale: A Green’s Function Plane Wave Code for Nanomaterials ORNL Electron Transport (ORe. Tran) Code Presented by Thomas C. Schulthess Computer Science and Mathematics Division Center for Nanophase Materials Sciences
Successful predictions of new materials Boron nitride nanotubes (predicted 1994, synthesized 1996) - Pseudopotential plane wave code 2 Fe/Mg. O/Fe magnetic tunnel junction (predicted 2001 at ORNL, synthesized 2004) - Layer-KKR and quantum transport code
Flowchart of ORe. Tran Start Initialization Fixed energy plane wave basis Parameters Block wave functions in the left and right leads For each energy For each K-point Integration of charge densities over K-points and energies End 3 Conductance. Plane wave propagation matrix in the middle region and nonequilibrium charge density Transmission and reflection matrices Conductance Keldysh Green function and nonequilibrium charge density Return
Tunable spin Hall effect 2 DES in x-z plane z x 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 4
Spin-polarized injections Wave densities for injected beam polarized along x or z direction Diffraction patterns (charge lattices) 5
Transverse charge current 0. 0015 0. 0010 j X Period of QD array: b = 20 nm Y Z 0. 0005 Width of QD array: 0 < a < 20 nm 0. 0000 - 0. 0005 0 5 10 a (nm) 15 20 Asymmetric diffraction transverse charge currents δj depends on spin polarization of injected beam 6
Selective polarization flipping 1. 0 Principal beam - j 0: Transmission - P 0: Polarization X 0. 9 Y Z j 0 Spin flipping for injection polarized along x or y 0. 8 0 7 5 10 a (nm) 15 20
Possible application Different transverse charge current from different spin-polarized injection: Spin current detector Principal beam with near-perfect transmission and high spin polarization Magnetic Random Access Memory 8
Non-spin-polarized injection Charge lattice (symmetric) 9 Spin lattice (anti-symmetric)
Transverse spin current 0. 005 0. 000 -0. 005 Period of QD array: b = 20 nm x j z j Width of QD array: 0 < a < 20 nm y j z -0. 010 zjz -0. 015 0 5 10 a (nm) 15 20 No transverse charge current Transverse spin currents defined outside the SO region Real, dissipative, and detectable 10
Contacts Thomas Schulthess Oak Ridge National Laboratory (865) 574 -4344 schulthesstc@ornl. gov Gonzalo Alvarez Oak Ridge National Laboratory (865) 241 -5498 Alvarezcampg@ornl. gov Jun-Qiang Lu Oak Ridge National Laboratory (865) 574 -1956 luj 1@ornl. gov Xiaoguang Zhang Oak Ridge National Laboratory (865) 241 -0200 zhangx@ornl. gov 11 Schulthess_Dynamics_0611
