Electron bunching in stacks of coupled quantum dots

We study the transport properties of two double quantum dots in a parallel arrangement at temperatures of a few kelvin. Thereby, we show that decoherence entailed by the substrate phonons affects the shot noise. For asymmetric coupling between the dots and the respective lead, the current noise is sub-Poissonian for resonant tunneling, but super-Poissonian in the vicinity of the resonances. Our results indicate that the interaction between different channels together with phonon emission and absorption are responsible for the shot noise characteristics. The observed asymmetry of the peaks at low temperatures stems from spontaneous emission.

Figure 1

(Color online) Sketch of the transport through two parallel double quantum dots measured in Ref. 10. Both transport channels are capacitively coupled. The source-drain voltage shifts the relative position of the levels by $eV$; albeit it is so large that all levels lie within the voltage window.

Figure 2

(a) Differential conductance, current (inset), and (b) Fano factor through a single channel for various temperatures and ${\Gamma }_L=0.025$, ${\Gamma }_R=0.0125$, $\Omega =0.025$, $\epsilon =0.5$, and $\alpha =0.005$ (in meV). The inset of panel (b) shows the Fano factor for dissipation strength $\alpha =0$ (solid), ${10}^{-3}$ (dotted), and ${10}^{-2}$ (dashed) at zero temperature.

Figure 3

(a) Differential conductance and (b) Fano factor for two coupled channels for various temperatures and the parameters ${\Gamma }_L=0.025$, ${\Gamma }_R=0.0125$, $\Omega =0.025$, $\alpha =0.005$, ${\epsilon }_1=0.5$, and ${\epsilon }_2=0.75$ (in meV). The inset shows the temperature broadening of the current peak.

Figure 4

(a) Differential conductance and (b) Fano factor for two coupled channels for various temperatures and the parameters ${\Gamma }_L=0.11$, ${\Gamma }_R=0.055$, $\Omega =0.11$, $\alpha =0.005$, ${\epsilon }_1=0.5$, and ${\epsilon }_2=0.75$ (in meV). The inset shows the temperature broadening of the current peak.

Figure 5

(Color online) Phonon-assisted channel opening: The blocking electron in the off-resonant channel can tunnel through the interdot barrier after phonon absorption (left) or emission (right) and thereby open the resonant channel.