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The relation between noise and Fick diffusion coefficient in barrier limited transport of particles obeying the asymmetric simple exclusion processes is physically assessed by Monte Carlo simulations. For a closed ring consisting of a large number of barriers the diffusion coefficient is related explicitly to the current noise thus revealing the existence of a generalized Nyquist-Einstein relation. For an open linear chain of barriers the diffusion coefficient is no longer related to current noise and depends on particle concentration but is independent of barrier number. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

In the case of a series of N identical diodes it is usually argued that the Fano factor should be suppressed by a factor 1/N with respect to the full shot value ascribed to the single diode. To discuss the limits of validity of this conjecture, we consider a simple two terminal device of N tunnel barriers, generating shot noise. In the absence of correlations among carriers, the application of Carson theorem gives full shot noise in the limit of vanishing frequency, contrary to the above conjecture. The results of Monte Carlo simulations, on a series of two and more tunnel barriers, confirm that for independent current pulses full shot noise is obtained in the limit of vanishing frequencies, as dictated by Carson theorem. When repulsive correlations among carriers are introduced, the simulations evidence the onset of shot noise suppression. We notice that the presence of different time scales in the system, as well as the unavoidable presence of 1/f noise can make the resolution of the vanishing frequency limit difficult to be achieved experimentally. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The low frequency current spectral density and the Fano factor of a double barrier resonant diode are investigated in the case of coherent tunneling as a function of voltage just below the current peak. At for voltages near the current peak the Fano factor is predicted to become suppressed below the value of 0.5. This drop below 0.5 is interpreted as an indication of coherent against sequential tunneling transport. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]