Minimal realization of the Orbital Kondo effect in a Quantum Dot with two Leads

TL;DR

This paper theoretically explores the minimal conditions for observing the orbital Kondo effect in a quantum dot with two leads, highlighting the roles of level degeneracy, temperature, and electron spin in different Kondo regimes.

Contribution

It introduces a minimal model for the orbital Kondo effect in quantum dots, analyzing conductance behavior at various temperatures and degeneracies, including the SU(2) and SU(4) Kondo effects.

Findings

Conductance peaks at degeneracy for high temperatures

Zero conductance at zero temperature at SU(2) symmetric point

Unitary conductance at finite level splitting for SU(2)

Abstract

We demonstrate theoretically how the Kondo effect may be observed in the transport of spinless electrons through a quantum dot. The role of conduction electron spin is played by a lead index. The Kondo effect takes place if there are two close levels in the dot populated by a single electron. For temperatures exceeding the Kondo temperature $T\gg T_K$ the conductance is maximal if the levels are exactly degenerate. However, at zero temperature the conductance is zero at the SU(2) symmetric point, but reaches the unitary limit $G = e^2/h$ for some finite value of the level splitting $\Delta\eps\sim T_K$. Introducing the spin-1/2 for electrons and having two degenerate orbital levels in the dot allows to observe the SU(4) Kondo effect in a single dot coupled to two leads.