Nonequilibrium effect in an electron turnstile

When an electron tunnels into a quantum dot, it may be stuck in a state higher than the lowest available singe-particle level. Equilibration with a lead is greatly slowed down by the Coulomb blockade in the dot and Pauli exclusion in the lead at low temperatures. This may produce heating of an electron turnstile or pump, if the intradot relaxation rate is slow compared with the pumping frequency. These ideas are demonstrated by simple models with realistic parameters, and the effect of phonon-induced intradot transitions is estimated in some detail.