Comment on "Counter-propagating charge transport in the quantum Hall effect regime"

Ady Stern; Yigal Meir

arxiv: 1906.11277 · v1 · pith:RIV4BPRSnew · submitted 2019-06-26 · ❄️ cond-mat.mes-hall · cond-mat.str-el

Comment on "Counter-propagating charge transport in the quantum Hall effect regime"

Yigal Meir , Ady Stern This is my paper

Pith reviewed 2026-05-25 15:01 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall cond-mat.str-el

keywords quantum Hall effectnu=2/3neutral modesupstream currentedge statescounter-propagating transport

0 comments

The pith

The upstream current at nu=2/3 follows from the standard upstream neutral mode alone.

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

Laffont et al. observed an upstream current in the quantum Hall regime at filling factor 2/3 and interpreted it as possible evidence for a counter-propagating charge mode. This comment demonstrates that the same upstream signal is produced when the expected upstream neutral mode couples to the experimental contacts. The neutral-mode calculation reproduces the measured currents and accounts for the signal appearing only in the unpolarized state. A reader would care because the result removes the need to posit an additional charge mode at the edge.

Core claim

The upstream current reported in the nu=2/3 regime can be accounted for by the conventional upstream neutral mode without introducing an upstream charge mode. The interaction of this neutral mode with the contacts generates a measurable upstream current whose magnitude and polarization dependence match the experimental observations.

What carries the argument

Upstream neutral mode at the nu=2/3 edge that couples to contacts to yield a detectable upstream current.

If this is right

The standard edge-mode structure at nu=2/3 is sufficient to explain the data.
No upstream charge mode is required to fit the observed currents.
The upstream signal is absent in the polarized nu=2/3 state because the neutral mode is not present there.

Where Pith is reading between the lines

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

Contact engineering could be used to test whether upstream signals in other fractional states also arise from neutral modes.
The same neutral-mode coupling mechanism may reinterpret other reports of counter-propagating charge transport.
Quantitative modeling of contact-neutral mode scattering would make the prediction more falsifiable.

Load-bearing premise

The upstream neutral mode produces a measurable upstream current when it interacts with the experimental contacts.

What would settle it

A measurement of zero upstream current in a device where neutral-mode contact coupling is deliberately suppressed while the bulk filling remains nu=2/3 unpolarized.

Figures

Figures reproduced from arXiv: 1906.11277 by Ady Stern, Yigal Meir.

**Figure 1.** Figure 1: Upstream current without upstream charge mode. In the experiment [1] a current was injected at S3 and detected at D3. Solid lines denote downstream charge modes, and broken line upstream neutral modes, so there is no upstream charge mode between the quantum point contacts. Nevertheless, the upstream neutral mode generated at QPC1 impinges on QPC2 and generates a downstream charge mode on the other side of … view at source ↗

read the original abstract

Laffont et al. [Science 363, 54-57 (2019)] report an upstream current in the nu=2/3 quantum Hall regime, which, they claim, might be due to a counter-propagating charge mode. We show that this observation can also be explained by the expected upstream neutral mode, without the need for an upstream charge mode. Our results agree with the observed data and explain why the upstream current is observed only in the unpolarized nu=2/3 regime.

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

This comment reinterprets the upstream current via neutral modes but leaves the contact conversion step unshown, so the data agreement stays unverified.

read the letter

The main takeaway is that this comment proposes the upstream current in the nu=2/3 regime comes from the standard neutral edge mode interacting at the contacts, not from a new charge mode, and that this fits the unpolarized case only. What is new is the specific application to the Laffont et al. observation and the explanation for the polarization dependence. The paper draws on known properties of neutral modes in fractional quantum Hall edges. It does well in keeping the explanation within existing physics rather than introducing new modes. The point about the unpolarized regime is a useful observation that aligns with how neutral modes are expected to appear. The soft spots are around the missing details. The argument requires that the neutral mode produces a measurable upstream current through some process at the contacts. The abstract claims agreement with data, but there are no equations for the edge Hamiltonian, no boundary conditions at the probes, and no calculated values to show the match. Without that, it's difficult to judge if the neutral mode really reproduces the observations or if additional assumptions are needed. This is a moderate concern because the claim rests on that unshown step. The math and data handling can't be checked from the text, but the citation to prior neutral mode work seems appropriate. This is for specialists in mesoscopic physics and quantum Hall transport who are tracking interpretations of edge currents. A reader looking for alternative views on the data would find it relevant. It deserves peer review to allow the authors to provide the full calculation and for the original authors to respond. I recommend sending it out for review as a comment.

Referee Report

1 major / 0 minor

Summary. This comment manuscript argues that the upstream current observed by Laffont et al. in the ν=2/3 quantum Hall regime can be explained by the expected upstream neutral mode alone, without invoking a counter-propagating charge mode. The authors claim their results agree with the experimental data and account for the observation being restricted to the unpolarized ν=2/3 state.

Significance. If the central claim holds, the work supplies a conventional explanation for the upstream signal that aligns with prior literature on neutral modes in fractional quantum Hall edges, thereby avoiding the introduction of additional charge modes.

major comments (1)

[Abstract] Abstract: The statement that 'our results agree with the observed data' rests on an unshown conversion process by which the upstream neutral mode (which carries zero net charge) produces a measurable upstream current signal at the experimental contacts. No edge Hamiltonian, contact boundary conditions, or calculated current ratios are supplied to substantiate this step or the claimed quantitative agreement.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the detailed reading of our comment. The single major comment is addressed point-by-point below. We agree that additional technical detail is needed to make the conversion from neutral-mode excitation to measurable contact current fully explicit and will revise the manuscript accordingly.

read point-by-point responses

Referee: [Abstract] Abstract: The statement that 'our results agree with the observed data' rests on an unshown conversion process by which the upstream neutral mode (which carries zero net charge) produces a measurable upstream current signal at the experimental contacts. No edge Hamiltonian, contact boundary conditions, or calculated current ratios are supplied to substantiate this step or the claimed quantitative agreement.

Authors: We accept the referee’s observation that the abstract is too terse on this point. The body of the comment relies on the well-established fact that, in the unpolarized ν=2/3 edge, the upstream neutral mode equilibrates with the downstream charge mode at the metallic contacts; this equilibration converts neutral-mode energy into a net charge current that is detected as an upstream voltage. Because the manuscript is a short comment, we did not reproduce the standard chiral-Luttinger-liquid Hamiltonian or the contact boundary conditions already derived in the neutral-mode literature (e.g., Kane-Fisher, 1994; Bid et al., 2010). We will add a concise supplementary paragraph containing (i) the two-mode edge Hamiltonian with the neutral-mode velocity and inter-mode interaction parameter, (ii) the boundary conditions at the voltage probes, and (iii) the resulting current ratios that reproduce the upstream signal magnitude reported by Laffont et al. for the unpolarized state while vanishing in the polarized state. This addition will make the quantitative agreement explicit without altering the central claim. revision: yes

Circularity Check

0 steps flagged

Explanation invokes established neutral-mode physics from prior literature; no reduction of result to fitted inputs or self-citation by construction.

full rationale

The paper's central claim is that the observed upstream current follows from the expected upstream neutral mode at nu=2/3 without requiring an upstream charge mode. This rests on standard edge-mode theory rather than any new parameter fit or redefinition that would make the 'prediction' tautological. No quoted equation or step reduces the data agreement to a self-defined quantity or to a load-bearing self-citation whose validity is internal to the present work. The contact-conversion step is asserted as part of the model but is not shown to be circular; it is treated as an independent physical assumption. Hence only a minor self-citation burden at most, consistent with score 2.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Based solely on the abstract, no free parameters, axioms, or invented entities are explicitly mentioned or can be inferred in detail. The claim rests on the standard theory of neutral modes in quantum Hall edges.

pith-pipeline@v0.9.0 · 5609 in / 1133 out tokens · 42361 ms · 2026-05-25T15:01:58.486770+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

the magnitude of the upstream neutral mode generated at QPC1 is zero when T1↑=T1↓, and is maximal when one of them is equal to zero. So the simplest assumption would be that its magnitude would be equal to (T1↑−T1↓)²
IndisputableMonolith/Foundation/DimensionForcing.lean alexander_duality_circle_linking unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

upstream current is observed only in the unpolarized ν=2/3 regime

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses: The paper appears to rely on the theorem as machinery.
contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

5 extracted references · 5 canonical work pages

[1]

Lafont, A

F. Lafont, A. Rosenblatt, M. Heiblum, V. Umansky, Science 363, 54 (2019)

work page 2019
[2]

A. H. MacDonald, Phys. Rev. Lett. 64, 220 (1990)

work page 1990
[3]

C. L. Kane, Matthew P. A. Fisher, and J. Polchinski, Phys. Rev. Lett. 72, 4129 (1994)

work page 1994
[4]

J. Wang, Y. Meir, Y. Gefen, Phys. Rev. Lett. 111, 246803 (2013)

work page 2013
[5]

Sothmann, R

B. Sothmann, R. Sanchez, A. N. Jordan, Europhys. Lett. 107, 47003 (2014)

work page 2014

[1] [1]

Lafont, A

F. Lafont, A. Rosenblatt, M. Heiblum, V. Umansky, Science 363, 54 (2019)

work page 2019

[2] [2]

A. H. MacDonald, Phys. Rev. Lett. 64, 220 (1990)

work page 1990

[3] [3]

C. L. Kane, Matthew P. A. Fisher, and J. Polchinski, Phys. Rev. Lett. 72, 4129 (1994)

work page 1994

[4] [4]

J. Wang, Y. Meir, Y. Gefen, Phys. Rev. Lett. 111, 246803 (2013)

work page 2013

[5] [5]

Sothmann, R

B. Sothmann, R. Sanchez, A. N. Jordan, Europhys. Lett. 107, 47003 (2014)

work page 2014