Spin-orbit interaction in semiconductor quantum dots systems Sergio Ulloa et al. Department of Physics and Astronomy and Nanoscale and Quantum Phenomena Institute Ohio University Athens, OH

Spin-orbit interaction in semiconductors Effective magnetic field perp. to P: Spin precession along its path Strong and tunable electric fields on the electronic system Rashba field appearing from a top gate Side gates can generate lateral fields  quantum point contacts

Datta-Das spin transistor 1. Spin-polarized electron injection from a ferromagnetic (FM) source 2. Manipulation of spin via top-gate-controlled spin-orbit coupling 3. Detection of spin-polarized electrons via FM drain Datta & Das, APL 56, 665 (1990)

Electrical spin injection Schmidt et al., PRL 92, 226601 (2004) Suppression of electron spin polarization at finite voltage Large variation of experimental results Controlled, high spin injection so far elusive

Spin-orbit effects in … quantum dots rings  Aharonov-Casher and Aharonov-Bohm effects quantum point contacts  lateral spin-orbit fields

Lateral SO in QPCs – P. Debray half-plateau only for VERY asymmetric QPC potentials InAs GaAs QPC field dependence InAs B in plane B perpendicular

QPC + SO  Full polarization? Anh Ngo + SEU strongly asymmetric potential in QPC polarization? yes, but weak … half-plateau only if strong Zeeman field larger polarization possible but no half plateau

Interactions needed: NEGF calculation J. Wan + M. Cahay – U Cinci

Dots-in-ring ϕσ=ϕAB+σϕSO M. Heiblum Aharonov-Bohm flux allow measurement of relative phases SO spin-dependent phases become relevant even if leads are unpolarized how is the Kondo effect in such a dot affected by SO and AB phases? ϕσ=ϕAB+σϕSO recent expts in AB+SO (p-type GaAs) Grbc et al PRL 2007 theory ……..

Dot-in-ring once around: the importance of symmetry Edson Vernek + Nancy Sandler + SEU single-particle self-energy for QD orbital depends on AB and SO phases only through ϕσ … but relative amplitude of the effect depends on V2 strong particle-hole asymmetry

Dot-in-ring – turn on interactions in the dot: U=0.5, εd=-U/2 NRG calculations increasing ϕSO quickly destroys Kondo screening Kondo peak decreases for both spin species local moment increases reducing V2 reduces the effect akin to local Zeeman field?

Including a local Zeeman field restores Kondo screening

Spin filtering in the Kondo regime