Kondo effect and spin filtering in triangular artificial atoms

TL;DR

This paper investigates the Kondo effect in triangular artificial atoms, revealing symmetry-driven orbital degeneracy leading to an SU(4) Kondo state and exploring the effects of magnetic fields and singlet-triplet transitions.

Contribution

It introduces the concept of symmetry-driven orbital degeneracy causing an SU(4) Kondo state in triangular artificial atoms, and analyzes the effects of magnetic fields on Kondo states.

Findings

SU(4) Kondo state with phase shift π/4 due to orbital degeneracy

Orbital Kondo state with smaller Kondo temperature under Zeeman field

Measurable Kondo temperatures in triangular artificial atoms

Abstract

We study strongly correlated states in triangular artificial atoms. Symmetry-driven orbital degeneracy of the single particle states can give rise to an SU(4) Kondo state with entangled orbital and spin degrees of freedom, and a characteristic phase shift $\delta = \pi/4$. Upon application of a Zeeman field, a purely orbital Kondo state is formed with somewhat smaller Kondo temperature and a fully polarized current through the device. The Kondo temperatures are in the measurable range. The triangular atom also provides a tool to systematically study the singlet-triplet transitions observed in recent experiments.