  Kondo-type zero-bias anomalies have been frequently observed in quantum dots
occupied by two electrons and attributed to a spin-triplet configuration that
may become stable under particular circumstances. Conversely, zero-bias
anomalies have been so far quite elusive when quantum dots are occupied by an
even number of electrons greater than two, even though a spin-triplet
configuration is more likely to be stabilized there than for two electrons. We
propose as an origin of this phenomenon the spin-orbit interaction, and we show
how it profoundly alters the conventional Kondo screening scenario in the
simple case of a laterally confined quantum dot with four electrons.
