Shot noise in mesoscopic transport through localised states

Abstract

We show that shot noise can be used for studies of hopping and resonant tunnelling between localised electron states. In hopping via several states, shot noise is seen to be suppressed compared with its classical Poisson value S I ¼ 2eI (I is the average current) and the suppression depends on the distribution of the barriers between the localised states. In resonant tunnelling through a single impurity an enhancement of shot noise is observed. It has been established, both theoretically and experimentally, that a considerable increase of noise occurs due to Coulomb interaction between two resonant tunnelling channels.

Finite-size effect in shot noise in hopping conduction

“…As briefly discussed in the introduction, the shot noise in long samples is not universal and averages out in the limit L ≫ L C [11,12,13,16]. Below we discuss the shot noise in the most interesting limit L ∼ L C .…”

“…With this goal we chose the frequencies at least two orders of magnitude higher than in previous experiments [11,12,16]. Also the heterostructure used was relatively clean, so that the samples did not exhibit sizeable mesoscopic fluctuations even at low-T and strong depletion.…”

“…On one hand, the numerical results [15] suggest that in short samples the Fano factor remains sub-Poissonian (F ≈ 0.7). On the other hand, the experiments do not exclude the full Poissonian noise value in sub-micrometer sized samples [11,16].…”

A numerical study of Coulomb interaction effects on 2D hopping transport

“…The similar behavior might be expected for 2D hopping, because the long-range correlations, apparently responsible for the difference between α and 1, should be suppressed by Coulomb interaction effects, provided that the conductor length L is larger than a certain crossover length determined by the interaction constant χ. Unfortunately, recent experiments [8,31,32] could not help in answering this question; while giving a reliable confirmation of the shot noise suppression in longer conductors, their accuracy is not sufficient to resolve a possible (relatively minor) deviation of α from 1.…”

Shot Noise Suppression and Enhancement at 2D Hopping and in Single-Electron Arrays

“…The power p is found to depend slightly on the electric field. For the smallest field accessible for numerical study the exponent p is close to 1.5, the value recently observed experimentally at 2D hopping in mesoscopic samples [10]. At moderately low frequencies, the noise spectral density as a function of f develops a plateau.…”