Valley blockade and multielectron spin-valley Kondo effect in silicon

We report on the valley blockade and the multielectron Kondo effect generated by an impurity atom in a silicon nanofield effect device. According to the spin-valley nature of tunneling processes, and consistently with those allowed by the valley blockade regime, the manifestation of Kondo effect at occupation $N=1,2,3$ has the periodicity 4 of the electron filling sequence typical of silicon. The spin-valley Kondo effect emerges under different kinds of screening depending on the electron filling. By exploiting the valley blockade regime, valley index conservation in the Kondo SU(4) is deduced with no need of an external magnetic field. Microwave irradiation suppresses the Kondo effect at occupancies up to three electrons.