Out-of-Equilibrium Kondo Effect: Response to Pulsed Fields

The current in response to a rectangular pulsed bias potential is calculated exactly for a special point in the parameter space of the nonequilibrium Kondo model. Our simple analytical solution shows the all essential features predicted by the noncrossing approximation, including a hierarchy of time scales for the rise, saturation, and fall-off of the current; current oscillations with a frequency of eV/hbar; and the instantaneous reversal of the fall-off current for certain pulse lengths. Rich interference patterns are found for a nonzero magnetic field (either dc or pulsed), with several underlying time scales. These features should be observable in ultra small quantum dots.