Pith. sign in

REVIEW 3 major objections 5 minor 16 references

A quantum Hall edge coupled to a superconductor can reflect electrons back as holes in the same spin channel, and the process survives in the fully spin-polarized ν=1 regime only because particle loss violates the unitarity that would other

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗

Same-spin Andreev reflections occur at quantum Hall–superconductor interfaces, and particle loss enables them in the spin-polarized ν=1 regime.

T0 review reviewed 2026-08-01 challenge →

load-bearing objection A careful spin-resolved study with a strong ν=2 result; the ν=1 loss-enabled claim is plausible but underdetermined — the unproven 2×2 symmetry lemma and the admitted local ν=2 doping both need referee attention. the 3 major comments →

arxiv 2607.26487 v1 pith:G4USWOG2 submitted 2026-07-29 cond-mat.mes-hall cond-mat.supr-con

Same-spin Andreev reflections in the quantum Hall regime: the role of loss

Chun-Chia Chen , Jordan T. McCourt , John Chiles , Lingfei Zhao , Kenji Watanabe , Takashi Taniguchi , Fran\c{c}ois Amet , Antonio L. R. Manesco
show 2 more authors
Harold U. Baranger Gleb Finkelstein
This is my paper
classification cond-mat.mes-hall cond-mat.supr-con PACS 73.43.-f74.45.+c
keywords Andreev reflectionquantum Hallspin flipchiral Andreev edge statesparticle lossnon-Hermiticityrandom matrix theoryspin polarization
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

The reading

This paper presents transport evidence that Andreev reflection at a quantum Hall–superconductor interface can flip spin, sending electrons back as holes in the same spin channel. In the fully spin-polarized ν=1 case, theory says this should be impossible: a unitary, particle-hole symmetric scattering matrix with no topology must be diagonal. The authors observe it anyway and argue that particle loss into the superconductor (quasiparticles absorbed by vortices or leaked into normal contacts) breaks the unitarity constraint. They support this with exponential statistics of reflection probabilities, a random-matrix model with loss channels, and tight-binding simulations. If right, the result means non-Hermiticity—not just spin-orbit coupling—must be considered in any hybrid quantum Hall–superconductor device, including proposals for chiral Majorana modes.

Core claim

The central claim is that Andreev reflections at a quantum Hall–superconductor interface can flip electron spin, producing a hole in the same spin channel, and that at ν=1 this is enabled by particle loss. In the lossless limit, the ν=1 scattering matrix is 2×2, particle-hole symmetric, unitary, and non-topological, forcing the electron-to-hole conversion amplitude to zero; adding loss (modeled as many extra effective channels) relaxes the constraint, and the authors observe spin-up holes in the outgoing spin-up channel. Evidence includes the sign structure of the spin-resolved downstream resistance R_d↑/R_d↓ and the P_eh histograms, which show bipolar distributions in both spin channels and

What carries the argument

The chiral Andreev edge state (CAES), the hybrid electron-hole mode formed at the quantum Hall–superconductor interface, is measured through spin-resolved downstream resistances R_d↑ and R_d↓ and converted to the probability difference P_eh = P_e − P_h. The theoretical engine is random matrix theory: strong loss is modeled by adding many weakly coupled effective channels, making the S-matrix large, so individual matrix elements become Gaussian-distributed and the observed exponential histograms follow. The load-bearing no-go result is that a lossless ν=1 S-matrix that is unitary, particle-hole symmetric, and has determinant 1 must be diagonal in the particle-hole basis, so same-spin Andreev

Load-bearing premise

The experiment assumes the ν_L = ν_R = 1 spin polarizers are ideal—they transmit only spin-up electrons and fully block spin-down with no leakage or spin-mixing—so if they leak, the observed same-spin holes could be ordinary opposite-spin Andreev reflections sneaking through the filter.

What would settle it

Measure the spin-resolved downstream resistance at ν=1 in a device whose polarizer has been independently characterized to have, say, >10^3 extinction ratio, while the superconductor contact is made nearly lossless (for example, by minimizing vortices or using a short, high-quality interface). If negative R_d↑ persists in this low-loss limit, the loss-enabling claim is weakened; if it vanishes, the claim is confirmed. Alternatively, directly detect a hole in the spin-up channel using a spin-sensitive detector such as a quantum point contact tuned across the ν=1→ν=2 transition.

Watch this falsifier. Get emailed when new claim-graph text bears on it.

If this is right

  • Proposals for chiral Majorana modes in quantum Hall–superconductor hybrids must explicitly account for loss; a same-spin hole signal alone is not evidence of a topological e↑/h↑ mode.
  • The exponential P_eh distributions and the near-constant ratio α_h/α_e ≈ 0.5 across magnetic field point to spin-orbit coupling inside the superconductor as the spin-flip source, not the interface.
  • Strong loss decorrelates the two spin channels, so the independence of R_d↑ and R_d↓ can serve as a diagnostic of loss in future devices.
  • The ν=1 and ν=2 results look nearly identical because loss channels dominate over the single extra edge channel, meaning loss sets the effective transport scales in these junctions.

Where Pith is reading between the lines

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

  • A clean, low-loss device at ν=1 should show far fewer same-spin holes; this is a testable difference from a genuinely topological e↑/h↑ mode and could be probed by engineering the vortex density or contact transparency.
  • The same 'loss breaks the no-go' logic may apply to other forbidden processes in spin-polarized edge states, such as crossed Andreev reflection or spin conversion in fractional quantum Hall edges, suggesting a general design principle for non-Hermitian topological hybrids.
  • If loss is the enabler, then the magnetic-field independence of α_h/α_e is surprising and worth checking at higher fields where vortex effects and loss rates change substantially.
  • The exponential, single-parameter distribution of reflection probabilities could be used as a fast experimental fingerprint to distinguish loss-enabled processes from coherent topological ones in other superconducting junctions.
Share X Bluesky LinkedIn Reddit HN

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

3 major / 5 minor

Summary. The paper reports spin-resolved transport measurements of chiral Andreev edge states (CAES) at a quantum Hall–superconductor interface in graphene. The device uses ν=1 regions as spin polarizers, injects spin-up electrons into a central region tuned to ν=2 or ν=1, and measures downstream resistances in the same and opposite spin channels. The main experimental claims are: (i) spin-flip processes accompany Andreev reflection, so that an incoming spin-up electron can emerge as a hole in the same spin-up channel; (ii) the distribution of the electron–hole imbalance P_eh is exponential, with the electron-side and hole-side decay rates differing by a factor of about two; (iii) at ν=1, where ordinary Andreev reflection is expected to be suppressed, holes in the spin-up channel nevertheless appear, and the authors attribute this to particle loss into the superconductor, invoking non-Hermiticity as the enabling mechanism. The paper includes random-matrix theory for the exponential distribution, Landauer–Büttiker modeling of the measurement schemes, and tight-binding simulations with a loss reservoir.

Significance. If the central claims hold, this is a significant advance. It would provide the first spin-resolved observation of same-spin Andreev reflection at a QH–SC interface, quantify spin-flip scattering through the ratio of electron and hole decay rates, and demonstrate that particle loss can lift the unitary suppression of Andreev reflection in a fully spin-polarized ν=1 edge. The claim has direct implications for proposals to realize chiral Majorana modes in QH–SC hybrids and for the role of non-Hermitian physics in topological superconductors. The paper has notable strengths: the data are openly available, the tight-binding calculations use a reproducible Kwant implementation, and the authors cross-check their measurement interpretation with several Landauer–Büttiker setups and a supplementary spin-filter test on a second device. These elements make the paper unusually transparent. However, the most striking claim—that loss, rather than local doping, enables the ν=1 signal—is not yet established by the evidence presented.

major comments (3)
  1. [Results, paragraph beginning 'Finally, we note that local doping likely exists...'] The ν=1 loss-enabled claim is undermined by the doping confound acknowledged in this paragraph. The authors observe a magnon gap indicating a local ν=2 region near the contact, and the ν=1 and ν=2 P_eh histograms in Fig. 4b are nearly identical. The response that even with doping h↑ is suppressed without loss cites Ref. [29], a 2×2 S-matrix lemma. That lemma applies only when the full scattering problem has a single electron and a single hole channel. A local ν=2 puddle adds a spin-down electron channel, making the BdG S-matrix at least 4×4 (two spins × electron/hole); the lemma then imposes no prohibition on e↑→h↑. The authors' own ν=2 data demonstrate h↑ without invoking loss. Thus the experiment does not isolate loss as the enabler; the data are equally explained by ordinary ν=2 Andreev reflection in a doped region. The tight-binding simulation in Fig. 4c,d includes loss by constructi
  2. [Results, 'The left and right regions...' and Fig. 1; Supp. S2] The spin-resolved measurement assumes the ν=1 polarizers are ideal, transmitting only spin-up and fully blocking spin-down. Under this assumption, negative R_d↑ is evidence of same-spin holes. If a polarizer leaks or spin-mixes, an ordinary opposite-spin hole h↓ can contribute to R_d↑ and mimic same-spin Andreev reflection. The supplementary two-device test (Fig. S2) is a useful cross-check, but it is performed on a different device and provides no quantitative leakage bound. Because the central spin-flip claim rests on the sign structure of R_d↑/R_d↓, the authors should report an upper bound on polarizer leakage or an in-situ check that the spin-up and spin-down channels are cleanly separated in the main device.
  3. [Results, 'We can now quantify the strength...' and Fig. 3a inset] The exponential form and the field-independent ratio α_h/α_e ≈ 0.5 are central quantitative results. The fits to the log-linear histograms are shown without error bars, confidence intervals, or goodness-of-fit statistics, and α_e and α_h are free parameters of the RMT model rather than predictions. Reporting fit uncertainties (e.g., bootstrap or χ²) would substantiate both the exponential claim and the statement that α_h/α_e is 'nearly constant' in magnetic field. Without them, the distinction between an exponential and a slightly curved distribution, and between a constant ratio and a weakly varying one, cannot be assessed.
minor comments (5)
  1. [References / Ref. [29]] Ref. [29] is an inline lemma in the reference list rather than a conventional citation. It should be moved to the main text or an appendix with a proof, and its domain of validity (number of electron/hole channels) should be stated explicitly.
  2. [Throughout] There are several typos: 'corrspond' in the RMT section, 'matirx' in Supplementary S0.7, 'acompanied' in the caption of Fig. 2e, and 'an and' in the introduction. A careful proofread is needed.
  3. [Eq. (1)] The conversion from R_d to P_eh is given for the unpolarized case; the spin-resolved extension is relegated to the supplementary. A one-line statement of the spin-resolved formula in the main text would improve readability.
  4. [Fig. 4a] The magnon emission gap is indicated by a white dashed line but is not quantitatively discussed. Please specify the threshold current and how the gap position is extracted.
  5. [Inset, Fig. 3a] The inset reports α_h/α_e versus magnetic field without error bars. Adding error bars or confidence intervals would make the claimed field independence testable.

Circularity Check

0 steps flagged

No significant circularity: the RMT exponential account fits decay constants rather than predicting them; the ν=1 loss argument rests on a 2×2 lemma proved in the supplement; the acknowledged doping confound is a validity issue, not a circular reduction.

full rationale

The paper's central quantitative claim—that the P_eh histograms are two-sided exponentials—is an empirical observation that is modeled by Eq. (4) with α_e and α_h as free parameters; the text explicitly says it uses RMT to "account for" the observation, not to predict the decay rates, and the exponential form is cited to external RMT results [35-37]. The ν=1 loss-enabled mechanism is not circular: the suppression of e↑→h↑ without loss follows from an independent 2×2 particle-hole/unitarity lemma, and the supplement supplies the proof ("Satisfying these conditions requires |s_he|=0"). The tight-binding simulation introduces loss through a finite superconducting segment, and only the width W=25 nm is tuned to survival probabilities; the sign statistics, bipolar histograms, and channel independence are not fitted targets. The paper itself flags the key experimental limitation—"local doping likely exists near the superconducting contact"—and asserts that the symmetry argument survives doping [29]; the quoted lemma is stated only for a 2×2 S-matrix, so extrapolation to a locally doped, possibly 4×4 system is an experimental-isolation weakness. That is a scientific validity concern, not a derivation that reduces to its own inputs. No fitted parameter is renamed as a prediction, and load-bearing citations to prior work are external published results with stated assumptions that do not include the target claim.

Axiom & Free-Parameter Ledger

3 free parameters · 5 axioms · 0 invented entities

The central claims rest mainly on the experimental conversion of R_d to P_eh (verified via Landauer-Büttiker cross-checks) and on two theoretical pillars: the RMT exponential distribution (with fitted α's) and the symmetry argument that loss enables ν=1 AR (stated as a lemma without proof). No new physical entities are introduced; loss is modeled via effective channels and a metallic drain in simulations.

free parameters (3)
  • α_e = not specified (varies with B; α_h/α_e ≈ 0.5)
    Decay rate for electron emission probability in the exponential P_eh distribution, fitted to the positive-P_eh side of histograms in Fig. 3a.
  • α_h = not specified (varies with B; α_h/α_e ≈ 0.5)
    Decay rate for hole emission probability, fitted to the negative-P_eh side of histograms; the ratio α_h/α_e is extracted and found nearly constant.
  • SC width W in simulation = 25 nm
    Width of the superconducting region in the tight-binding simulation, tuned to reproduce experimental survival probabilities (Supp. Sec. 0.8).
axioms (5)
  • standard math A 2×2 S-matrix that is particle-hole symmetric, unitary, and non-topological (det=1) must be diagonal in the particle-hole basis, so Andreev reflection vanishes at ν=1 without loss.
    Stated as ref. [29] without proof in the main text; load-bearing for the ν=1 loss argument.
  • standard math For a large random S-matrix, the distribution of a single matrix element's squared modulus is exponential with mean α ∝ 1/N (Eq. 2, from Refs. [35-37]).
    Used to derive the exponential P_eh distribution; standard RMT result cited to external literature.
  • domain assumption Loss can be modeled by adding a large number of weakly coupled fictitious channels, making the effective S-matrix large and random.
    Invoked in Supp. Sec. 0.7 to justify the RMT treatment; based on Büttiker voltage-probe and Brouwer-Baranger models.
  • domain assumption The disorder in the QH-SC interface and vortices in the superconductor produce a maximally random S-matrix (class D/CRE) and provide the dominant quasiparticle loss.
    Assumed throughout to justify both the RMT ensemble and the loss mechanism; supported by prior work [11,14,16].
  • domain assumption The tight-binding Hamiltonian (Eq. S12) with the chosen parameters accurately describes the graphene QH-SC hybrid.
    The simulation model is standard (Kwant, honeycomb lattice, BdG) but the specific parameter choices (E_Z, m_i, Δ, disorder) are selected to mimic the experimental regime.

reviewed 2026-08-01 · how reviews work

0 comments
Cite this review

Pith. "Pith review of Same-spin Andreev reflections in the quantum Hall regime: the role of loss." pith.science (2026). https://pith.science/paper/G4USWOG2

@misc{pith2026260726487,
  author       = {Pith},
  title        = {Pith review of: Same-spin Andreev reflections in the quantum Hall regime: the role of loss},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/G4USWOG2}},
  note         = {Machine review of arXiv:2607.26487}
}
Share X Bluesky LinkedIn Reddit HN
read the original abstract

The interfaces of superconductors and topological materials hold promise for realizing exotic states and excitations. An important example is provided by the chiral Andreev edge states (CAES), which are formed at interfaces between quantum Hall (QH) states and superconductors (SC). CAES combine electron and hole amplitudes which are hybridized via Andreev reflections. This study explores the spin properties of the CAES through selective spin filtering of the QH edge channels. We find robust evidence of spin-flips accompanying the Andreev processes: electrons can be reflected from the superconductor as holes in the same spin channel. We demonstrate that the distribution of the reflection probabilities is exponential and then use random matrix theory to account for this observation. Finally, we observe Andreev reflections in the spin-polarized {\nu} = 1 case, which is enabled by particle loss. Our findings shed light on the mechanism underlying Andreev reflections of spin-polarized chiral states. They also demonstrate the importance of considering non-Hermiticity when constructing topological superconductors in hybrid materials.

Figures

Figures reproduced from arXiv: 2607.26487 by Antonio L. R. Manesco, Chun-Chia Chen, Fran\c{c}ois Amet, Gleb Finkelstein, Harold U. Baranger, John Chiles, Jordan T. McCourt, Kenji Watanabe, Lingfei Zhao, Takashi Taniguchi.

Figure 1
Figure 1. Figure 1: FIG. 1. a) Schematic of the sample. The left and right regions are kept at [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. a,b) [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. a) [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. a) Downstream resistance [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

16 extracted references · 10 canonical work pages

  1. [1]

    Efetov, Di S

    Gil-Ho Lee, Ko-Fan Huang, Dmitri K. Efetov, Di S. Wei, Sean Hart, Takashi Taniguchi, Kenji Watanabe, Amir Yacoby, and Philip Kim. Inducing superconducting correlation in quantum Hall edge states.Nat. Phys., 13(7):693–698, Jul 2017.doi:10.1038/nphys4084

    doi:10.1038/nphys4084 2017

  2. [2]

    Arnault, Alexey Bondarev, Andrew Seredinski, Trevyn F

    Lingfei Zhao, Ethan G. Arnault, Alexey Bondarev, Andrew Seredinski, Trevyn F. Q. Larson, Anne W. Draelos, Hengming Li, Kenji Watanabe, Takashi Taniguchi, Fran¸ cois Amet, Harold U. Baranger, and Gleb Finkelstein. Interference of chiral Andreev edge states.Nat. Phys., 16(8):862–867, May 2020. doi:10.1038/s41567-020-0898-5

    work page doi:10.1038/s41567-020-0898-5 2020

  3. [3]

    Wei, Toeno van der Sar, Javier D

    Di S. Wei, Toeno van der Sar, Javier D. Sanchez-Yamagishi, Kenji Watanabe, Takashi Taniguchi, Pablo Jarillo-Herrero, Bertrand I. Halperin, and Amir Yacoby. Mach-Zehnder interferometry using spin- and valley-polarized quantum Hall edge states in graphene.Sci. Adv., 3(8):e1700600, 2017. URL: https://www.science.org/doi/abs/10.1126/sciadv.1700600,doi:10.1126...

    work page doi:10.1126/sciadv.1700600 2017

  4. [4]

    Arnault, Trevyn F

    Lingfei Zhao, Ethan G. Arnault, Trevyn F. Q. Larson, Kenji Watanabe, Takashi Taniguchi, Fran¸ cois Amet, and Gleb Finkelstein. Nonlocal transport measurements in hybrid quantum Hall–superconducting devices.Phys. Rev. B, 109(11):115416, Mar 2024. URL:https://link.aps.org/doi/10.1103/ PhysRevB.109.115416,doi:10.1103/PhysRevB.109.115416

    work page doi:10.1103/physrevb.109.115416 2024

  5. [5]

    C. W. J. Beenakker. Random-matrix theory of Majorana fermions and topological superconductors. Rev. Mod. Phys., 87:1037–1066, Sep 2015. URL:https://link.aps.org/doi/10.1103/RevModPhys. 87.1037,doi:10.1103/RevModPhys.87.1037

    doi:10.1103/revmodphys 2015

  6. [6]

    B¨ uttiker

    M. B¨ uttiker. Role of quantum coherence in series resistors.Phys. Rev. B, 33(5):3020–3026, March 1986. URL:https://link.aps.org/doi/10.1103/PhysRevB.33.3020,doi:10.1103/PhysRevB.33.3020

    work page doi:10.1103/physrevb.33.3020 1986

  7. [7]

    Baranger and Pier A

    Harold U. Baranger and Pier A. Mello. Effect of phase breaking on quantum transport through chaotic cavities.Phys. Rev. B, 51(7):4703–4706, February 1995. URL:http://link.aps.org/doi/10.1103/ PhysRevB.51.4703,doi:10.1103/PhysRevB.51.4703

    work page doi:10.1103/physrevb.51.4703 1995

  8. [8]

    P. W. Brouwer and C. W. J. Beenakker. Effect of a voltage probe on the phase-coherent conductance of a ballistic chaotic cavity.Phys. Rev. B, 51(12):7739–7743, March 1995. URL:https://link.aps. org/doi/10.1103/PhysRevB.51.7739,doi:10.1103/PhysRevB.51.7739

    work page doi:10.1103/physrevb.51.7739 1995

  9. [9]

    C. W. J. Beenakker. Random-matrix theory of quantum transport.Rev. Mod. Phys., 69(3):731– 808, July 1997. arXiv:cond-mat/9612179. URL:http://arxiv.org/abs/cond-mat/9612179,doi: 10.1103/RevModPhys.69.731

    Pith/arXiv arXiv 1997

  10. [10]

    Pereyra and P

    P. Pereyra and P. A. Mello. Marginal distribution of the S-matrix elements for Dyson’s measure and some applications.J. Phys. A, 16(2):237, February 1983.doi:10.1088/0305-4470/16/2/007

    work page doi:10.1088/0305-4470/16/2/007 1983

  11. [11]

    Meckes.The Random Matrix Theory of the Classical Compact Groups

    Elizabeth S. Meckes.The Random Matrix Theory of the Classical Compact Groups. Cambridge Univ. Press, Cambridge UK, 2019. URL:https://www. cambridge.org/core/books/random-matrix-theory-of-the-classical-compact-groups/ 06D446A342AACF0214BA492B49237394,doi:10.1017/9781108303453

    doi:10.1017/9781108303453 2019

  12. [12]

    M. L. Polianski and P. W. Brouwer. Scattering matrix ensemble for time-dependent transport through a chaotic quantum dot.J. Phys. A, 36(12):3215, March 2003.doi:10.1088/0305-4470/36/12/321

    work page doi:10.1088/0305-4470/36/12/321 2003

  13. [13]

    Groth, Michael Wimmer, Anton R

    Christoph W. Groth, Michael Wimmer, Anton R. Akhmerov, and Xavier Waintal. Kwant: A software package for quantum transport.New J. Phys., 16(6):063065, 2014. URL:http://stacks.iop.org/ 1367-2630/16/i=6/a=063065,doi:10.1088/1367-2630/16/6/063065

    doi:10.1088/1367-2630/16/6/063065 2014

  14. [14]

    Antonio L. R. Manesco, Ian Matthias Fl´ or, Chun-Xiao Liu, and Anton R. Akhmerov. Mechanisms of Andreev reflection in quantum Hall graphene.SciPost Phys. Core, 5(3):045, 2022. URL:https: //scipost.org/10.21468/SciPostPhysCore.5.3.045,doi:10.21468/SciPostPhysCore.5.3.045. 10

    work page doi:10.21468/scipostphyscore.5.3.045 2022

  15. [15]

    Antonio L. R. Manesco, I. M. Fl´ or, Chun-Xiao Liu, and Anton R. Akhmerov. Mechanisms of Andreev reflection in quantum Hall graphene, March 2021.doi:10.5281/zenodo.4597080

    work page doi:10.5281/zenodo.4597080 2021

  16. [16]

    Kurilovich, Zachary M

    Vladislav D. Kurilovich, Zachary M. Raines, and Leonid I. Glazman. Disorder-enabled An- dreev reflection of a quantum Hall edge.Nat. Commun., 14(1):2237, Apr 2023.doi:10.1038/ s41467-023-37794-1. 11

    2023

This paper was first reviewed by deepseek-v4-flash on August 1, 2026.