Quantum Dot Spin Filter in Resonant Tunneling and Kondo Regimes

TL;DR

This paper investigates how quantum dots with spin-orbit interaction can serve as efficient spin filters, especially under resonant tunneling and Kondo regimes, by analyzing a minimal two-level model.

Contribution

It demonstrates the enhancement of spin polarization via resonant tunneling and explores the generation of large spin currents through the SU(4) Kondo effect in quantum dots.

Findings

Resonant tunneling significantly boosts spin polarization when level spacing is small.

The SU(4) Kondo effect induces large spin currents in the Coulomb blockade regime.

Level spacing less than Kondo temperature is crucial for large spin current generation.

Abstract

A quantum dot with spin-orbit interaction can work as an efficient spin filter if it is connected to N (> 2) external leads via tunnel barriers. When an unpolarized current is injected to a quantum dot from a lead, polarized currents are ejected to other leads. A two-level quantum dot is examined as a minimal model. First, we show that the spin polarization is markedly enhanced by resonant tunneling when the level spacing in the dot is smaller than the level broadening. Next, we examine the many-body resonance induced by the Kondo effect in the Coulomb blockade regime. A large spin current is generated in the presence of the SU(4) Kondo effect when the level spacing is less than the Kondo temperature.