Origin of the Anomalous Electronic Shot Noise in Atomic-Scale Junctions

Abstract

Fluctuations pose fundamental limitations in making sensitive measurements, yet at the same time, noise unravels properties that are inaccessible at the level of the averaged signal. In electronic devices, shot noise arises from the discrete nature of charge carriers and it increases linearly with the applied voltage according to the celebrated Schottky formula. Nonetheless, measurements of shot noise in atomic-scale junctions at high voltage reveal significant nonlinear (anomalous) behavior, which varies from sample to sample, and has no specific trend. Here, we provide a viable, unifying explanation for these diverse observations based on the theory of quantum coherent transport.Our formula for the anomalous shot noise relies on-and allows us to resolve-two key characteristics of a conducting junction: The structure of the transmission function at the vicinity of the Fermi energy and the asymmetry of the bias voltage drop at the contacts. We tested our theory on high voltage shot noise measurements on Au atomic scale junctions and demonstrated a quantitative agreement, recovering both the enhancement and suppression of shot noise as observed in different junctions. The good theory-experiment correspondence supports our modelling and emphasizes that the asymmetry of the bias drop on the contacts is a key factor in nanoscale electronic transport, which may substantially impact electronic signals even in incomplex structures.

Scattering theory of non-equilibrium noise and delta T current fluctuations through a quantum dot

“…Before fully tackling the case of a Breit-Wigner resonance, a first step to go beyond the constant transmission results is to include small deviations, performing an expansion near the Fermi energy, τ (ω) τ + ωτ . This was considered in a previous work [8,9] and we recover here similar results in the form…”

“…A recent experiment using atomic break junctions [4]-with an embedded hydrogen molecule between the leads-measured the noise signal, dubbed 'ΔT noise' (DTN) in this situation. This generated a lot of interest for this previously undocumented source of non-equilibrium noise, both from the experimental [5][6][7] and the theoretical [8][9][10][11][12][13] perspectives. Results from reference [4] were found to be in good agreement with the scattering theory of non-equilibrium noise (STN) for a Fermi liquid (often referred to as the Landauer-Büttiker noise formula), with the further assumption that the transmission coefficient τ is constant over characteristic energy/temperature ranges, which is well justified here as hydrogen bounds well with the metallic leads.…”

“…Results from reference [4] were found to be in good agreement with the scattering theory of non-equilibrium noise (STN) for a Fermi liquid (often referred to as the Landauer-Büttiker noise formula), with the further assumption that the transmission coefficient τ is constant over characteristic energy/temperature ranges, which is well justified here as hydrogen bounds well with the metallic leads. A few theoretical works focused on going beyond this simple picture, by considering anomalous shot noise contributions, incorporating next order corrections [8,9] or looking at generalized forms of DTN, considering charge or heat shot noise in the absence of charge or heat currents respectively [13].…”

Determining Transmission Characteristics from Shot-Noise-Driven Electroluminescence in Single-Molecule Junctions

“…A lthough noise in measured electronic signals often decreases measurement sensitivity, shot noise provides a critical source of information about conducting devices. 1,2 Shot noise results from the discrete quantization of charge in the tunneling current. Measuring this fundamental property provides insight into a device's transmission channels beyond what can be inferred from conductance measurements alone.…”

“…Although noise in measured electronic signals often decreases measurement sensitivity, shot noise provides a critical source of information about conducting devices. , Shot noise results from the discrete quantization of charge in the tunneling current. Measuring this fundamental property provides insight into a device’s transmission channels beyond what can be inferred from conductance measurements alone. − However, due to the high frequencies of charge fluctuations, measuring shot noise typically requires fast measurement systems and/or cryogenic temperatures, ,,, although there are a few exceptions. , In this work, we present an alternative approach, with all experiments done at room temperature and data acquisition rates of no faster than 100 kHz.…”