Abrupt disappearance and re-emergence of the SU(4) and SU(2) Kondo effects due to population inversion

The interplay of almost degenerate levels in quantum dots and molecular junctions with possibly different couplings to the reservoirs has lead to many observable phenomena, such as the Fano effect, transmission phase slips, and the SU(4) Kondo effect. Here we predict a dramatic repeated disappearance and re-emergence of the SU(4) and anomalous SU(2) Kondo effects with increasing gate voltage. This phenomenon is attributed to the level occupation switching which has been previously invoked to explain the universal transmission phase slips in the conductance through a quantum dot. We use analytical arguments and numerical renormalization group calculations to explain the observations and discuss their experimental relevance and dependence on the physical parameters.