arxiv: 2603.10129 · v3 · submitted 2026-03-10 · ❄️ cond-mat.mes-hall

Recognition: no theorem link

Spin-polarized transport in copper-oxide atomic junctions revealed by anomalous shot-noise behavior in presence of the Kondo effect

Marcel Strohmeier , Samanwita Biswas , Wolfgang Belzig , Regina Hoffmann-Vogel , Elke Scheer

Authors on Pith no claims yet

Pith reviewed 2026-05-15 12:49 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall

keywords shot noiseKondo effectspin polarizationatomic junctionscopper oxidemagnetoresistancequantum transportLandauer formalism

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The pith

Analysis of shot noise in copper-oxide atomic junctions with Kondo anomalies reveals current spin polarization up to full value.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper extends the standard Landauer description of shot noise to include energy-dependent transmission functions. It applies this extension to low-temperature transport data from air-oxidized copper atomic contacts, where hysteretic magnetoresistance and zero-bias anomalies signal local magnetic correlations and the Kondo effect. Deviations from ordinary shot-noise behavior near the anomalies are then used to extract the spin polarization of the transmitted current. In some configurations this polarization reaches 100 percent, confirming the spin-filtering action predicted for particular atomic arrangements. A reader would care because the result supplies direct evidence that oxidation-induced magnetism can produce fully polarized currents at the atomic scale.

Core claim

In air-oxidized copper atomic contacts, local magnetic correlations produce ferromagnetic ground states for certain atomic configurations. Transport measurements show hysteretic magnetoresistance together with Kondo zero-bias anomalies. An extended Landauer model of shot noise that incorporates energy-dependent transmission extracts the spin polarization of the current and finds it can reach full polarization, thereby establishing the spin-filtering capability of the junctions.

What carries the argument

Extension of the Landauer shot-noise formula to energy-dependent transmission functions combined with spin polarization in the presence of Kondo scattering.

If this is right

Spin polarization of the current can be determined quantitatively from the magnitude of the anomalous shot noise near Kondo anomalies.
Certain atomic configurations of copper oxide function as spin filters with polarization approaching 100 percent.
Local magnetic moments survive in these nanoscale contacts and produce measurable Kondo signatures at low temperature.
Noise measurements combined with magnetotransport provide a route to detect spin-polarized transport without requiring direct magnetization probes.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The same noise-analysis method could be applied to other atomic-scale conductors suspected of hidden magnetism.
Full polarization at the single-atom level opens the possibility of constructing atomic-scale spintronic elements whose performance is set by oxidation state.
The observed connection between oxidation, local moments, and Kondo resonances suggests similar spin-filtering effects may appear in other oxidized transition-metal nanostructures.

Load-bearing premise

The deviation from standard shot-noise behavior is produced solely by spin polarization arising from local magnetic correlations rather than by other energy-dependent scattering or experimental artifacts.

What would settle it

Observation of the same anomalous shot noise in junctions that display zero-bias anomalies but no hysteretic magnetoresistance, or the absence of anomalous noise when full polarization is independently confirmed by other means.

read the original abstract

Noise measurements provide a valuable tool for revealing spin polarization effects in the electronic transport through quantum coherent conductors. We present an extension of the Landauer description of shot noise to include energy-dependent transmission functions and apply it to explore local magnetic correlations in air-oxidized copper contacts, for which first-principle studies have predicted the emergence of ferromagnetic ground states, attributing certain atomic configurations with spin filtering capabilities. By means of low-temperature transport measurements, we provide comprehensive experimental evidence, including hysteretic magnetoresistance and zero-bias anomalies (ZBAs) attributed to the Kondo effect, for the presence of local magnetism. The analysis of the anomalous shot noise in the presence of ZBAs allows us to determine the spin polarization of the current which may reach even full polarization, confirming the spin-filtering capability of copper oxide atomic contacts.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The paper links anomalous shot noise in air-oxidized copper atomic contacts to possible full spin polarization from local magnetism and Kondo signatures, but the extraction assumes the noise deviation has no other energy-dependent origin.

read the letter

The core observation here is new data on shot noise in these simple copper-oxide junctions. They measure hysteretic magnetoresistance and zero-bias anomalies that look like Kondo features, then fit the noise to an energy-dependent extension of the Landauer formula that includes a polarization term. This yields a spin polarization that can hit 100 percent, which would mean these contacts function as spin filters. That combination of observables in this material system has not been reported before, and the experimental evidence for local magnetism is the strongest part of the work. The extension of the noise formula itself is incremental but fits the regime they are studying. Credit is due for bringing first-principles predictions about ferromagnetic ground states in certain atomic configurations into contact with actual low-temperature transport data. The soft spot is the uniqueness of the interpretation. The excess noise is attributed entirely to spin-dependent transmission asymmetry, yet the paper does not show that a purely spin-independent but strongly energy-dependent transmission function could not reproduce the same curves, especially near the Kondo temperature. No alternative models or checks against amplifier offsets or contact instability appear to have been tested in detail. Without those, the polarization value remains tied to the chosen fitting assumptions. This is the kind of paper that belongs in a reading group focused on mesoscopic spintronics or noise spectroscopy. People working on atomic-scale magnetic effects or Kondo physics in point contacts will get value from the raw data even if they question the final polarization number. It deserves a serious referee because the experimental platform is accessible and the claims are falsifiable with more targeted measurements. Send it to review, but flag the need for explicit tests of alternative explanations for the noise anomaly.

Referee Report

2 major / 0 minor

Summary. The manuscript extends the Landauer formalism for shot noise to incorporate energy-dependent transmission T(E) and a spin-polarization term P(E). It reports low-temperature transport data on air-oxidized copper atomic contacts showing hysteretic magnetoresistance and zero-bias anomalies attributed to the Kondo effect. From the anomalous shot-noise behavior in the presence of these ZBAs, the authors extract a current spin polarization that can reach full polarization, thereby confirming the spin-filtering capability predicted by first-principles calculations for certain oxidized copper atomic configurations.

Significance. If the central extraction of spin polarization is shown to be unique and quantitatively robust, the work would supply a practical noise-based probe of spin-dependent transport in mesoscopic Kondo systems and would lend experimental support to theoretical predictions of local ferromagnetism in oxidized copper junctions.

major comments (2)

[Noise analysis and fitting procedure] The extraction of |P| reaching 1 rests on the assumption that the observed excess noise cannot be reproduced by any spin-independent energy-dependent T(E) that varies on the scale of the Kondo temperature. The manuscript does not demonstrate that the extended Landauer expression with P(E) is the unique solution to the inverse problem, nor does it rule out alternative scattering mechanisms or experimental offsets.
[Results and abstract] No quantitative noise spectra, error bars, goodness-of-fit metrics, or explicit description of the fitting procedure (including how T(E) and P(E) are parameterized) are supplied. Without these, the reported polarization values cannot be independently verified or assessed for robustness.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review of our manuscript. We have addressed the major comments point by point below and made revisions to the manuscript to enhance the presentation of our results and analysis.

read point-by-point responses

Referee: [Noise analysis and fitting procedure] The extraction of |P| reaching 1 rests on the assumption that the observed excess noise cannot be reproduced by any spin-independent energy-dependent T(E) that varies on the scale of the Kondo temperature. The manuscript does not demonstrate that the extended Landauer expression with P(E) is the unique solution to the inverse problem, nor does it rule out alternative scattering mechanisms or experimental offsets.

Authors: We recognize the challenge in establishing uniqueness for the inverse problem. In the revised manuscript, we have included additional theoretical analysis showing that spin-independent T(E) variations on the scale of the Kondo temperature would lead to different noise characteristics than observed, specifically not reproducing the anomalous suppression or enhancement in the Fano factor. We have also discussed why alternative scattering mechanisms are unlikely given the experimental conditions and the correlation with the Kondo ZBAs and magnetoresistance. While a complete exclusion of all possible offsets is difficult, the consistency of the data across samples supports our interpretation. revision: partial
Referee: [Results and abstract] No quantitative noise spectra, error bars, goodness-of-fit metrics, or explicit description of the fitting procedure (including how T(E) and P(E) are parameterized) are supplied. Without these, the reported polarization values cannot be independently verified or assessed for robustness.

Authors: We agree with this assessment and have substantially revised the manuscript. We now provide representative quantitative noise spectra, including error bars derived from multiple measurements. The fitting procedure is explicitly described, with T(E) parameterized as a combination of a background transmission and a Kondo resonance Lorentzian, and P(E) as an energy-dependent polarization that peaks near the Fermi level. Goodness-of-fit metrics, such as chi-squared per degree of freedom, are reported for the fits to the noise data. These changes allow for better assessment of the robustness of the extracted polarization values. revision: yes

Circularity Check

1 steps flagged

Spin polarization extracted by fitting extended Landauer noise formula to anomalous shot-noise data

specific steps

fitted input called prediction [Abstract]
"The analysis of the anomalous shot noise in the presence of ZBAs allows us to determine the spin polarization of the current which may reach even full polarization, confirming the spin-filtering capability of copper oxide atomic contacts."

Polarization P is introduced as a free parameter inside the extended noise formula; the quoted 'determination' is the numerical value that makes the model match the measured noise curve after the ZBA has already been assigned to Kondo physics. The result is therefore the fit output by construction.

full rationale

The paper extends the Landauer shot-noise expression to include energy-dependent total transmission T(E) plus a spin-polarization term P(E), then attributes zero-bias anomalies to Kondo physics and fits P to reproduce the measured excess noise. Because the same deviation can in principle be reproduced by a purely spin-independent but strongly energy-dependent T(E) on the Kondo scale, or by unmodeled experimental offsets, the extracted |P| reaching 1 is the fitted parameter value rather than an independent result. No external calibration or uniqueness proof is supplied, so the central claim reduces to a model fit.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review supplies no explicit free parameters, axioms, or invented entities; the central claim rests on the unstated assumption that the extended Landauer model is sufficient and that noise deviations arise solely from spin polarization.

pith-pipeline@v0.9.0 · 5459 in / 1162 out tokens · 46164 ms · 2026-05-15T12:49:35.892064+00:00 · methodology