Prediction of femtosecond oscillations in the transient current of a quantum dot in the Kondo regime

We invoke the time-dependent noncrossing approximation in order to study the effects of the density of states of gold contacts on the instantaneous conductance of a single electron transistor which is abruptly moved into the Kondo regime by means of a gate voltage. For an asymmetrically coupled system, we observe that the instantaneous conductance in the Kondo time scale exhibits beating with distinct frequencies, which are proportional to the separation between the Fermi level and the sharp features in the density of states of gold. Increasing the ambient temperature or bias quenches the amplitude of the oscillations. We attribute the oscillations to interference between the emerging Kondo resonance and van-Hove singularities in the density of state. In addition, we propose an experimental realization of this model.

Figure 1

(Color online) The total density of states of gold is shown by a black curve as a function of the separation from the Fermi level. The bold red curve corresponds to the best fit to the ab initio data by a linear combination of Gaussian functions, which are represented by thin green curves.

Figure 2

(Color online) The gray, red, and orange curves (from top to bottom) show the instantaneous conductance versus time in the Kondo time scale after the dot level has been switched to its final position for asymmetry factors of 0.85, 0.9, and 0.95, respectively, at $T=0.009{\Gamma }_{tot}$ and $V=T_K$ for constant ${\Gamma }_{tot}$.

Figure 3

(Color online) The red, blue, and black curves (from top to bottom) represent the instantaneous conductance versus time in the Kondo time scale after the dot level has been switched to its final position for an asymmetry factor of 0.9 at $T=0.009{\Gamma }_{tot}$ when the bias is equal to $V=T_K$, $V=4T_K$, and $V=8T_K$, respectively, for constant ${\Gamma }_{tot}$.

Figure 4

(Color online) The green, black, blue, red, and purple curves (from top to bottom) represent the instantaneous conductance versus time in the Kondo time scale after the dot level has been switched to its final position for an asymmetry factor of 0.9 at $T=0.0015{\Gamma }_{tot}$, $T=0.0030{\Gamma }_{tot}$, $T=0.0060{\Gamma }_{tot}$, $T=0.0090{\Gamma }_{tot}$, and $T=0.0150{\Gamma }_{tot}$, respectively, for constant ${\Gamma }_{tot}$ with a bias of $V=T_K$.