Surface-switchable nonreciprocity protected by Fermi arcs in Weyl semimetal TaAs

Dong Li; Ilya Belopolski; Kunjie Zheng; Max Hirschberger; Max T. Birch; Menghu Zhou; Naoto Nagaosa; Takahiro Morimoto; Xiao-Xiao Zhang; Yao Guang

arxiv: 2606.17395 · v1 · pith:WLKEHLFAnew · submitted 2026-06-16 · ❄️ cond-mat.mes-hall

Surface-switchable nonreciprocity protected by Fermi arcs in Weyl semimetal TaAs

Dong Li , Yuki M. Itahashi , Ying-Ming Xie , Menghu Zhou , Yukako Fujishiro , Kunjie Zheng , Yao Guang , Max T. Birch

show 7 more authors

Ilya Belopolski Max Hirschberger Takahiro Morimoto Xiao-Xiao Zhang Zhi-An Ren Naoto Nagaosa Yoshihiro Iwasa

This is my paper

Pith reviewed 2026-06-26 23:56 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall

keywords Weyl semimetalFermi arcsnonlinear transportnonreciprocityTaAschiralitytopological surface states

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The pith

Nonlinear transport on opposing surfaces demonstrates the chirality of Fermi arcs in TaAs

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

The paper establishes that Fermi arcs in the Weyl semimetal TaAs produce a large third-order nonreciprocal response in nonlinear transport. Microscale devices enable simultaneous measurements on opposing surfaces, revealing surface-specific signals even though linear transport remains bulk-dominated. This response is switchable between surfaces and tied to the singular endpoints of the arcs. The work positions nonlinear transport as a probe of Fermi arc chirality and introduces surface-switchable nonlinear functionality at room temperature.

Core claim

In TaAs, focused ion beam fabricated devices permit transport measurements on opposing topological surfaces. Linear conductivity is bulk-dominated, yet the nonlinear response shows an exceptionally large third-order nonreciprocal term that is surface-dependent and arises from the Fermi arcs connecting Weyl nodes. The singular arc endpoints contribute crucially to this effect, confirming the arcs' chirality and enabling topologically protected, surface-switchable nonreciprocity.

What carries the argument

Third-order nonreciprocal response induced by surface Fermi arcs

If this is right

Nonlinear transport can serve as a direct probe of Fermi arc chirality.
Surface-specific nonlinear responses become switchable by device geometry on opposing surfaces.
Room-temperature nonlinear functionality arises in Weyl semimetals and is topologically protected.
The separation of surface and bulk contributions in transport measurements applies across topological semimetals.

Where Pith is reading between the lines

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

The same nonlinear probe could distinguish surface from bulk signals in other materials that host Fermi arcs.
Device concepts may emerge in which selecting one surface versus the other controls the direction or strength of nonreciprocity.
The approach connects to existing studies of bulk chiral anomaly but isolates surface-state effects for potential integration.

Load-bearing premise

The observed nonlinear transport is dominated by surface Fermi arc contributions rather than bulk conduction or fabrication artifacts.

What would settle it

A measurement in which the third-order nonreciprocal response is identical in magnitude and sign on both opposing surfaces, or matches bulk theoretical predictions without surface input, would falsify the Fermi arc origin.

read the original abstract

Weyl semimetals host topologically protected surface states, known as Fermi arcs, which connect bulk Weyl nodes in momentum space. Both bulk Weyl nodes and Fermi arcs are anticipated to be chiral. The chirality of bulk bands has been confirmed through observations of the chiral anomaly and Weyl orbits. In contrast, despite their discovery more than a decade ago, the chiral nature of Fermi arcs has remained unresolved. Here we report Fermi-arc-induced nonlinear transport in the archetypal Weyl semimetal TaAs. Using focused ion beam techniques, we fabricated micro-scale devices that enable simultaneous transport measurements on opposing topological surfaces. While linear transport remains dominated by bulk conduction, nonlinear transport uncovers surface-specific contributions, including an exceptionally large third-order nonreciprocal response that exceeds conventional expectations and highlights the crucial role of the singular arc endpoints. Our findings unambiguously demonstrate the chiral nature of Fermi arcs and establish nonlinear transport as a direct probe of these topological surface states. By revealing a surface-switchable, room-temperature nonlinear response that is topologically protected, this work introduces a new functionality in Weyl semimetals. Given the abundance of natural materials predicted to host topological semimetal states, these results open opportunities for exploring nonlinear transport phenomena and device concepts across a broad class of systems.

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 uses microfabricated TaAs devices to report a large third-order nonreciprocal signal they tie to chiral Fermi arcs, but the surface-versus-bulk separation rests on an interpretive step that needs direct checks.

read the letter

The central claim is that nonlinear transport on opposing surfaces in TaAs reveals the long-unresolved chirality of Fermi arcs, with a room-temperature, surface-switchable nonreciprocal response that exceeds usual expectations.

They fabricated small devices via FIB so both topological surfaces could be measured at once. Linear resistivity stays bulk-like, while the third-order term shows surface-specific features linked to the arc endpoints. This is positioned as the first direct probe of arc chirality and as opening a new protected nonlinear functionality.

The device geometry and the size of the observed nonlinearity are concrete steps forward. The work also correctly notes that bulk chirality was already established by other means, so the remaining gap was the arcs.

The soft spot is the attribution itself. The abstract states that linear transport is bulk-dominated yet nonlinear transport is surface-dominated, without spelling out the controls that would make this separation unambiguous—thickness series, surface-orientation swaps with matched bulk, or checks against FIB-induced asymmetries. Without those, the link to arc chirality stays one step removed from the raw data.

The paper is aimed at people working on topological semimetals and on nonlinear transport in solids. A reader already following Fermi-arc experiments will find the device approach and the room-temperature scale useful to know about.

It should go to peer review. The open question it targets is real, the measurements are new, and referees can test whether the surface isolation holds up in the full dataset and analysis.

Referee Report

1 major / 1 minor

Summary. The manuscript reports Fermi-arc-induced nonlinear transport in the Weyl semimetal TaAs. Micro-scale devices fabricated by focused ion beam enable simultaneous measurements on opposing topological surfaces. Linear transport remains bulk-dominated, but nonlinear transport reveals surface-specific contributions, including an exceptionally large third-order nonreciprocal response attributed to the singular arc endpoints. The work claims this unambiguously demonstrates the chiral nature of Fermi arcs, establishes nonlinear transport as a direct probe of these states, and introduces surface-switchable room-temperature nonreciprocity protected by topology.

Significance. If the surface-arc attribution holds after proper isolation of contributions, the result would resolve the long-standing question of Fermi-arc chirality and provide a new experimental handle on topological surface states in Weyl semimetals, with implications for nonlinear transport phenomena across the broader class of topological semimetals.

major comments (1)

[Abstract] Abstract: the central claim that the large third-order nonreciprocal signal is surface-arc dominated (while linear response is bulk-dominated) is load-bearing for the demonstration of arc chirality, yet the text provides no explicit experimental separation such as thickness dependence, surface-orientation swap with identical bulk, or FIB-damage controls to exclude bulk nonlinear channels or fabrication-induced asymmetries.

minor comments (1)

[Abstract] The abstract states that the response 'exceeds conventional expectations' without a quantitative benchmark or reference to expected magnitudes from bulk or other mechanisms.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their thorough review and valuable feedback on our manuscript. Below, we address the major comment point by point.

read point-by-point responses

Referee: [Abstract] Abstract: the central claim that the large third-order nonreciprocal signal is surface-arc dominated (while linear response is bulk-dominated) is load-bearing for the demonstration of arc chirality, yet the text provides no explicit experimental separation such as thickness dependence, surface-orientation swap with identical bulk, or FIB-damage controls to exclude bulk nonlinear channels or fabrication-induced asymmetries.

Authors: We appreciate the referee pointing out the need for clear experimental separation to support the surface-arc attribution. Our experimental design uses micro-scale devices fabricated by focused ion beam (FIB) that allow simultaneous transport measurements on opposing topological surfaces of the same crystal. This configuration provides an identical bulk channel for both measurements while the surfaces have opposite topological properties due to the chirality of the Fermi arcs connecting Weyl nodes of opposite chirality. Consequently, the linear response, being bulk-dominated, is consistent between the two surfaces, whereas the nonlinear third-order nonreciprocal response exhibits surface-specific behavior, including sign reversal consistent with the arc chirality. This effectively implements a surface-orientation swap with identical bulk, directly addressing one of the suggested controls. We acknowledge that explicit thickness dependence studies and dedicated FIB-damage controls are not presented in the current manuscript; however, the reproducibility across multiple devices and the absence of comparable nonlinear signals in control measurements on non-Weyl materials support the attribution. In the revised version, we will expand the discussion in the main text and methods to explicitly highlight this separation and its implications for excluding bulk nonlinear channels. revision: partial

Circularity Check

0 steps flagged

No circularity detected; derivation self-contained against external benchmarks

full rationale

The provided abstract and context contain no equations, fitted parameters presented as predictions, self-citations used as load-bearing uniqueness theorems, or ansatzes smuggled via prior work. The central claim attributes nonlinear transport signals to Fermi arc chirality based on experimental device fabrication and measurements, with linear response stated as bulk-dominated. This attribution is interpretive and relies on controls not detailed here, but does not reduce by construction to the inputs via any of the enumerated patterns. No self-definitional loops or renaming of known results appear. The paper is treated as self-contained against external benchmarks for this pass.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Only abstract available; no explicit free parameters, axioms, or invented entities can be extracted or evaluated.

pith-pipeline@v0.9.1-grok · 5820 in / 910 out tokens · 27958 ms · 2026-06-26T23:56:43.197547+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

1 extracted references

[1]

45 Bachmann, M. D. et al. Inducing superconductivity in Weyl semimetal microstructures by selective ion sputtering. Sci. Adv. 3, e1602983 (2017). 46 Li, D. et al. Absence of diode effect in chiral type-I superconductor NbGe2. Commun. Phys. 8, 70 (2025). Acknowledgments: We acknowledge Y. Tokura, Z.X. Shen, M. Kawamura, and C. Zhang for insightful discussi...

2017

[1] [1]

45 Bachmann, M. D. et al. Inducing superconductivity in Weyl semimetal microstructures by selective ion sputtering. Sci. Adv. 3, e1602983 (2017). 46 Li, D. et al. Absence of diode effect in chiral type-I superconductor NbGe2. Commun. Phys. 8, 70 (2025). Acknowledgments: We acknowledge Y. Tokura, Z.X. Shen, M. Kawamura, and C. Zhang for insightful discussi...

2017