Minimal realization of the orbital Kondo effect in a quantum dot with two leads

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 $T⪢{T}_{K}$, 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 $\ensuremath{\Delta}\ensuremath{\epsilon}\ensuremath{\sim}{T}_{K}$. 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.