Non-Gaussian Current Fluctuations in a Short Diffusive Conductor

We report the measurement of the third moment of current fluctuations in a short metallic wire at low temperature. The data are deduced from the statistics of voltage fluctuations across the conductor using a careful determination of environmental contributions. Our results at low bias agree very well with theoretical predictions for coherent transport with no fitting parameter. By increasing the bias voltage we explore the crossover from elastic to inelastic transport.

Figure 1

Schematics of the experimental setup. A/D represents a 14 bits, 400 MSample/s digitizer.

Figure 2

Third moment of voltage fluctuations $S_{V^3}$ for the wire (purple) and the tunnel junction (orange) vs $I$. Symbols are experimental data; the solid line is a fit for the tunnel junction using Eq. (4) with $S_{I^3}=e^{2}I$, from which the environmental parameters are deduced. Inset: The second moment of current fluctuations $S_{I^2}$ vs $I$ (the noise of the amplifier has been subtracted for the sake of clarity).

Figure 3

Intrinsic third moment of current fluctuations $S_{I^3}$ vs $I$ for the wire at different temperatures. Symbols are experimental data, lines are the theoretical expectations of Eq. (2). Inset: $S_{I^3}$ for the tunnel junction (orange) and the wire (purple) for higher currents up to 0.3 mA at $T\sim 640\mathrm{mK}$.

Figure 4

(a) Fano factor of the second moment of current fluctuation $F_2=e^{-1}d{S}_{I^2}/dI$ for the wire vs $I$. (b) Fano factor of the third moment of current fluctuations $F_3=e^{-2}d{S}_{I^3}/dI$ for the wire vs $I$. Different symbols correspond to different temperatures ranging from 130 mK to 660 mK. The black lines correspond to the theoretical prediction in the elastic regime. Dashed (dotted dashed) line corresponds to the current for which $L_{e\text{−}e}=L$ ($L_{e\text{−}\mathrm{ph}}=L$).