Origin of the Anomalous Electronic Shot Noise in Atomic-Scale Junctions
Pith reviewed 2026-05-24 19:45 UTC · model grok-4.3
The pith
Anomalous shot noise in atomic-scale junctions is explained by the transmission function structure near the Fermi energy combined with bias voltage asymmetry at the contacts.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
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 impact even
What carries the argument
The derived expression for excess shot noise that incorporates the energy derivative of the transmission function near the Fermi energy and the fractional voltage drop at each contact.
If this is right
- Noise measurements can extract the local slope of the transmission function and the contact voltage asymmetry for a given junction.
- Both enhancement and suppression of shot noise are recovered by varying only those two parameters across different Au atomic contacts.
- Bias asymmetry remains important for transport signals even in simple atomic-scale structures.
- The same framework unifies observations that previously lacked a common trend.
Where Pith is reading between the lines
- The same transmission-plus-asymmetry model could be used to interpret noise data in molecular junctions or other mesoscopic conductors where direct spectroscopy is difficult.
- Device engineering that deliberately tunes contact asymmetry might offer a route to control noise levels without changing the average conductance.
- If the transmission function varies rapidly, the anomalous contribution could dominate at voltages still low enough that heating remains negligible.
Load-bearing premise
The junctions remain in the coherent quantum transport regime with no significant inelastic scattering or heating at the voltages used.
What would settle it
A measurement showing strong anomalous shot noise in an atomic junction whose transmission function is independently verified to be flat near the Fermi energy and whose contacts exhibit symmetric bias drop would contradict the explanation.
read the original 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.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript claims that the anomalous nonlinear shot noise observed in high-bias measurements on atomic-scale Au junctions originates from the energy dependence of the transmission function near the Fermi energy combined with asymmetry in the bias voltage drop, all within the standard coherent Landauer-Büttiker quantum transport formalism. The authors derive an explicit formula for the noise that depends on these two junction-specific characteristics, then demonstrate quantitative agreement with experimental data from multiple junctions, recovering both noise enhancement and suppression without invoking additional mechanisms.
Significance. If the central claim holds, the work supplies a unifying, parameter-light explanation for sample-to-sample variability in high-voltage shot noise using only established coherent-transport theory. The quantitative match to experiment on real Au junctions is a concrete strength that directly supports the modeling. The result would underscore that contact asymmetry can dominate noise behavior even in simple atomic structures, with potential consequences for noise-limited measurements and device design at the nanoscale.
major comments (2)
- [Theory derivation and experimental comparison] The derivation and comparison rest on the assumption that transport remains fully coherent with negligible inelastic scattering or local heating at the voltages employed (abstract, paragraph 3; theory section). No explicit bound is given on junction length versus inelastic mean free path, nor is there a calculation showing that electron-phonon contributions remain smaller than the reported anomalous term. This assumption is load-bearing for the claim that T(E) shape and bias asymmetry alone account for all observations.
- [Results and fitting procedure] The two key inputs (transmission-function shape near E_F and bias-asymmetry parameter) are determined by fitting to each sample's noise data. The manuscript should clarify whether these parameters can be independently constrained (e.g., from conductance or I-V curves alone) or whether the quantitative agreement is achieved only after sample-specific adjustment, which would weaken the predictive status of the formula.
minor comments (2)
- [Theory section] Notation for the bias-asymmetry parameter and the precise definition of the transmission function T(E) should be introduced once and used consistently; several equations reuse symbols without redefinition.
- [Figures] Figure captions would benefit from explicit statements of which curves correspond to which fitted parameter sets and whether error bars include only statistical or also systematic contributions.
Simulated Author's Rebuttal
We thank the referee for the detailed and constructive report. We address the major comments below and will revise the manuscript accordingly where appropriate.
read point-by-point responses
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Referee: [Theory derivation and experimental comparison] The derivation and comparison rest on the assumption that transport remains fully coherent with negligible inelastic scattering or local heating at the voltages employed (abstract, paragraph 3; theory section). No explicit bound is given on junction length versus inelastic mean free path, nor is there a calculation showing that electron-phonon contributions remain smaller than the reported anomalous term. This assumption is load-bearing for the claim that T(E) shape and bias asymmetry alone account for all observations.
Authors: We agree that an explicit justification of the coherent transport assumption would strengthen the paper. In the revised manuscript, we will add a discussion estimating the inelastic mean free path in Au at the experimental biases (typically >10 nm) relative to the ~1 nm junction length, and a simple estimate showing electron-phonon noise contributions are subdominant to the anomalous term from T(E) and bias asymmetry. revision: yes
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Referee: [Results and fitting procedure] The two key inputs (transmission-function shape near E_F and bias-asymmetry parameter) are determined by fitting to each sample's noise data. The manuscript should clarify whether these parameters can be independently constrained (e.g., from conductance or I-V curves alone) or whether the quantitative agreement is achieved only after sample-specific adjustment, which would weaken the predictive status of the formula.
Authors: The zero-bias conductance provides a direct constraint on T(E_F), but the energy dependence of T(E) near E_F and the bias asymmetry are indeed primarily determined from the noise measurements, as the I-V curves offer limited additional information on these details. We will revise the text to clarify this point and to emphasize that the fitted parameters then allow the model to predict the entire voltage dependence of the noise for each junction without further adjustment, thereby preserving the explanatory power of the approach. revision: partial
Circularity Check
Derivation self-contained in standard Landauer-Büttiker formalism; no load-bearing reduction to self-inputs or self-citations
full rationale
The paper derives its anomalous shot noise formula from the established theory of quantum coherent transport (Landauer-Büttiker), treating transmission function shape near E_F and bias asymmetry as junction-specific inputs that are fitted to match observed noise data. No equations or steps in the provided text reduce the central result to a tautology or to a self-citation chain; the quantitative agreement is presented as a test of the model rather than a prediction forced by construction. The coherent-transport assumption is an external modeling choice whose validity is separate from circularity. This is the normal case of a theory paper that introduces parameters to explain sample variation.
Axiom & Free-Parameter Ledger
free parameters (2)
- transmission function shape near E_F
- bias voltage asymmetry parameter
axioms (2)
- domain assumption Electron transport through the junction is coherent and described by the Landauer-Büttiker formalism
- domain assumption Inelastic scattering and heating are negligible at the voltages considered
discussion (0)
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