Enhanced Shot Noise in Resonant Tunneling via Interacting Localized States

In a variety of mesoscopic systems shot noise is seen to be suppressed in comparison with its Poisson value. In this work we observe a considerable enhancement of shot noise in the case of resonant tunneling via localized states. We present a model of correlated transport through two localized states which provides both a qualitative and a quantitative description of this effect.

Figure 1

(a) Resonant tunneling through a localized state in a barrier. (b) Cross section of the transistor structure with two Ohmic contacts and the gate between them. (c) Typical RT peaks in the Ohmic conductance at different temperatures.

Figure 2

(a) Conductance peaks in the region of $V_g$ where the current noise has been measured. (b) Excess noise power as a function of $V_{\mathrm{s}\mathrm{d}}$: at $V_g=-1.6945\mathrm{V}$ for $T=1.85\mathrm{K}$ and $V_g=-1.696\mathrm{V}$ for $T=4.2\mathrm{K}$. (The latter is offset for clarity.) Lines show the dependences $S_I(V_{\mathrm{s}\mathrm{d}})$ expected for resonant tunneling through a single impurity from Eq. (1), with $F=1$ (solid), $F=0.63$ (dashed), and $F=0.52$ (dotted). Inset: Excess noise spectrum at $V_g=-1.696\mathrm{V}$ and $V_{\mathrm{s}\mathrm{d}}=1.5\mathrm{m}\mathrm{V}$.

Figure 3

Left panel: Energy diagrams of the two impurities for different positive $V_{\mathrm{s}\mathrm{d}}$: $V_{\mathrm{s}\mathrm{d}}^{(1)}<V_{\mathrm{s}\mathrm{d}}^{(2)}<V_{\mathrm{s}\mathrm{d}}^{(3)}$. Inset: Schematic representation of the modulation of the current through impurity $R$ by changing the occupancy of modulator $M$. Main part: Gray-scale plot of the differential conductance as a function of $V_g$ and $V_{\mathrm{s}\mathrm{d}}$ at $T=1.85\mathrm{K}$ (darker regions correspond to higher differential conductance, background hopping contribution is subtracted). Lines show the positions of the conductance peaks of impurity $R$ and modulator $M$, obtained from the analysis.

Figure 4

Excess noise and the corresponding Fano factor as functions of source-drain bias at different gate voltages. (The noise data for different $V_g$ are offset for clarity.) Solid lines show the results of the numerical calculations.