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arxiv: 2307.14072 · v5 · pith:65ZYMCTBnew · submitted 2023-07-26 · ❄️ cond-mat.mes-hall · eess.SP· physics.app-ph· quant-ph

Negative Spin Delta_T noise Induced by Spin-Flip Scattering and Andreev Reflection

Sachiraj Mishra , Colin Benjamin This is my paper

Pith reviewed 2026-05-24 08:00 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall eess.SPphysics.app-phquant-ph
keywords Δ_T noisespin noiseAndreev reflectionspin-flip scatteringhybrid junctionsN-sf-N-I-S junctionsuperconducting devices
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0 comments X

The pith

Spin Δ_T noise reverses from positive to negative in N-sf-N-I-S junctions via spin-flip scattering and Andreev reflection.

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

The paper analyzes charge and spin Δ_T noise in a normal metal-spin flipper-normal metal-insulator-superconductor junction. While charge Δ_T noise stays positive, spin Δ_T noise changes sign to negative through the combined influence of spin-flip scattering and Andreev reflection. Quantum shot noise for both charge and spin remains positive and sign-definite. This sign reversal in spin Δ_T noise marks a distinction from shot noise and serves as a probe for the cooperative action of those two scattering processes.

Core claim

In the N-sf-N-I-S junction, spin Δ_T noise undergoes a sign reversal from positive to negative driven by the interplay between spin-flip scattering and Andreev reflection, whereas charge Δ_T noise remains strictly positive and both charge and spin quantum shot noise stay positive and sign-definite. The negative spin Δ_T noise is dominated by opposite-spin correlations and provides access to scattering mechanisms not captured by quantum shot noise alone.

What carries the argument

The spin Δ_T noise computed for the N-sf-N-I-S junction, where spin-flip scattering and Andreev reflection act together to produce the sign change.

If this is right

  • Negative spin Δ_T noise distinguishes spin-resolved Δ_T noise from quantum shot noise because the former is dominated by opposite-spin correlations while the latter is led by same-spin correlations.
  • Negative spin Δ_T noise provides access to scattering mechanisms that are not captured by quantum shot noise alone.
  • Negative spin Δ_T noise serves as a unique probe of the cooperative effects of Andreev reflection and spin flipping in superconducting hybrid devices.
  • The results can be placed in context with earlier reports of negative Δ_T noise in fractional quantum Hall states and multiterminal hybrid superconducting junctions.

Where Pith is reading between the lines

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

  • Detection of the sign reversal in spin Δ_T noise could be used to identify the presence of spin-flip processes in other hybrid superconducting structures.
  • The same modeling approach might be applied to noise in systems with different spin-dependent scattering strengths to predict additional sign changes.
  • Extending calculations to finite temperatures or bias voltages could test whether the negative regime persists under broader experimental conditions.

Load-bearing premise

The junction is modeled such that spin-flip scattering and Andreev reflection can be treated as independent scattering channels whose combined effect produces the reported sign change in spin noise.

What would settle it

A measurement of spin Δ_T noise in an N-sf-N-I-S device that shows no sign reversal when both spin-flip scattering and Andreev reflection are active would falsify the central claim.

Figures

Figures reproduced from arXiv: 2307.14072 by Colin Benjamin, Sachiraj Mishra.

Figure 1
Figure 1. Figure 1: Illustration of the 1D bilayer metallic junction, with a mag [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Illustration of different spin configurations when spin ↑ or ↓ electron encounters a spin-flipper with S = ±m or S , ±m. τ and τ1 are spin-flip probabilities for spin-up and spin-down incident electrons. When the electron’s elastic scattering time is much greater than the spin-flipper’s relaxation time τe ≫ τs f , the spin￾flipper will flip back before encountering the next incident electron, see [PITH_FU… view at source ↗
Figure 3
Figure 3. Figure 3: Schematic representation of a bilayer metallic junction [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: (a) ∆ η T , (b) |∆ η T sh/∆ η Tth|, and (c) ∆ η T sh(Tth) vs. J, where η = ch (black, dashed), sp (blue, dashed) and N IN (red, solid). Previous works on NIN junction, show that charge ∆T noise is always positive [12, 13, 15]. However, in this paper for a N1/SF/N2 junction with spin-flip scattering, the charge ∆ ch T noise can be negative due to the exchange interaction. On the other hand, ∆ sp T noise is … view at source ↗
Figure 5
Figure 5. Figure 5: Same-spin and opposite-spin correlation contributions to (a) [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Same-spin and opposite-spin correlation contributions to (a) [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
read the original abstract

We study charge $\Delta_T$ noise, followed by an examination of spin $\Delta_T$ noise, in the normal metal-spin flipper-normal metal-insulator-superconductor (N-sf-N-I-S) junction. Our analysis reveals a key contrast: while charge $\Delta_T$ noise remains strictly positive, spin $\Delta_T$ noise undergoes a sign reversal from positive to negative, driven by the interplay between spin-flip scattering as well as Andreev reflection. In contrast, charge quantum shot noise remains positive and sign-definite, which is also valid for spin quantum shot noise. The emergence of negative spin $\Delta_T$ noise has two major implications. First, it establishes a clear distinction between spin-resolved $\Delta_T$ noise and quantum shot noise: the former is dominated by opposite-spin correlations, whereas the latter is led by same-spin correlations. Second, it provides access to scattering mechanisms that are not captured by quantum shot noise alone. Thus, negative spin $\Delta_T$ noise serves as a unique probe of the cooperative effects of Andreev reflection and spin flipping. We further place our results in context by comparing them with earlier reports of negative $\Delta_T$ noise in strongly correlated systems, such as fractional quantum Hall states, and in multiterminal hybrid superconducting junctions. Overall, this work offers new insights into the mechanisms governing sign reversals in $\Delta_T$ noise and highlights their role as distinctive fingerprints of spin-dependent scattering in superconducting hybrid devices.

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.

Referee Report

1 major / 0 minor

Summary. The manuscript analyzes charge and spin Δ_T noise (temperature-difference driven current noise) in an N-sf-N-I-S junction. It reports that charge Δ_T noise remains strictly positive while spin Δ_T noise reverses sign from positive to negative due to the interplay of spin-flip scattering and Andreev reflection; both charge and spin quantum shot noise remain positive. The negative spin Δ_T noise is attributed to dominance of opposite-spin correlations and is positioned as a probe of cooperative scattering effects not accessible via shot noise, with comparisons to negative Δ_T noise in FQHE and multiterminal hybrids.

Significance. If the sign reversal is robustly derived, the result supplies a concrete distinction between spin-resolved Δ_T noise and shot noise, with the former sensitive to opposite-spin processes. This could serve as a diagnostic for Andreev-plus-spin-flip physics in hybrid devices and adds to the catalog of negative Δ_T noise phenomena.

major comments (1)
  1. [Abstract (and the derivation of the noise expressions)] The central claim of negative spin Δ_T noise requires that the scattering matrix (or Green's function) for the combined spin-flip and Andreev processes yields a noise correlator in which opposite-spin contributions dominate the integral. The manuscript must explicitly show the S-matrix composition or equivalent and verify that coherent multiple-scattering paths between the sf region and I-S interface are retained; an independent-channel treatment risks producing artificial negativity that a unitary calculation would eliminate.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their thorough review and valuable feedback on our work. We have carefully considered the major comment regarding the explicit demonstration of the scattering matrix and coherent paths. Our response is provided below, and we will make revisions to enhance clarity.

read point-by-point responses

  1. Referee: [Abstract (and the derivation of the noise expressions)] The central claim of negative spin Δ_T noise requires that the scattering matrix (or Green's function) for the combined spin-flip and Andreev processes yields a noise correlator in which opposite-spin contributions dominate the integral. The manuscript must explicitly show the S-matrix composition or equivalent and verify that coherent multiple-scattering paths between the sf region and I-S interface are retained; an independent-channel treatment risks producing artificial negativity that a unitary calculation would eliminate.

    Authors: We agree with the referee that an explicit demonstration of the S-matrix composition is necessary to confirm the retention of coherent paths. In our calculation, the scattering matrix for the entire junction is constructed by composing the spin-flip scattering matrix in the N-sf-N region with the Andreev reflection matrix at the I-S interface, using the standard composition rules for scattering matrices in series. This composition inherently includes all multiple reflection paths between the sf region and the I-S interface, as the intermediate normal metal segment allows for coherent propagation. The resulting S-matrix is unitary by construction, and the noise correlators are computed from the full expression involving the transmission and reflection probabilities for same and opposite spins. The negative spin Δ_T noise emerges when the opposite-spin Andreev processes, enhanced by spin-flips, dominate the integral over energy. We did not use an independent-channel approximation. To make this transparent, we will include in the revised version an explicit derivation of the composite S-matrix and a verification of its unitarity in an appendix or dedicated subsection. This will also clarify the abstract's claim by referencing the detailed derivation. revision: yes

Circularity Check

0 steps flagged

No circularity detected; derivation self-contained

full rationale

The provided abstract and context describe a scattering-based calculation of Δ_T noise in an N-sf-N-I-S junction, with the sign reversal of spin Δ_T noise attributed to the interplay of spin-flip scattering and Andreev reflection. No equations, fitted parameters, or self-citations are exhibited that reduce the reported negativity to a definition, a renamed input, or a load-bearing self-citation chain. The central contrast between charge (always positive) and spin (sign-reversing) noise is presented as an output of the model rather than an input. Absent any quoted reduction of the form 'prediction = fit by construction,' the derivation chain does not meet the criteria for circularity and is scored as self-contained.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review supplies no explicit free parameters, axioms, or invented entities; cannot populate ledger.

pith-pipeline@v0.9.0 · 5808 in / 1050 out tokens · 28856 ms · 2026-05-24T08:00:53.398260+00:00 · methodology

discussion (0)

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Reference graph

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