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arxiv: 2605.00359 · v1 · submitted 2026-05-01 · ❄️ cond-mat.mes-hall · cond-mat.mtrl-sci

Investigation of nonlocal transport associated with the orbital Hall effect in Ti

Keitaro Takashina , Naoki Yano , Asahi Oe , Mari Taniguchi , Shuto Kimura , Kazuya Ando This is my paper

Pith reviewed 2026-05-09 19:22 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall cond-mat.mtrl-sci
keywords orbital Hall effectnonlocal transportTi Hall barorbital currentnonlocal resistanceOhmic bypassmesoscopic transport
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0 comments X

The pith

Nonlocal resistance in single-layer Ti Hall bars exceeds what Ohmic bypass simulations predict, suggesting orbital transport from the orbital Hall effect.

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

The authors measure nonlocal voltage signals in titanium Hall bars that have negligible spin Hall effect, so any orbital contribution should stand out. They record a finite nonlocal resistance whose size changes with the width of the central channel. Finite-element models reproduce a large fraction of the signal as ordinary current leaking around the voltage probes, yet the measured values remain higher than the models even after resistivity variations are allowed. The mismatch points to an extra nonlocal channel that the authors attribute to orbital currents generated by the orbital Hall effect inside the titanium.

Core claim

In single-layer Ti Hall bars a nonlocal resistance persists after the Ohmic bypass contribution estimated from finite-element simulations is subtracted, and the discrepancy survives even when spatial variations in Ti resistivity are included; the residual signal is therefore interpreted as orbital-current transport driven by the orbital Hall effect.

What carries the argument

The comparison of measured nonlocal resistance versus central channel width against finite-element simulations that calculate the Ohmic bypass current in the Hall-bar geometry.

If this is right

  • Orbital currents could be generated and detected in light metals without heavy-element spin-orbit coupling layers.
  • Channel-width scaling offers a practical method to separate orbital from charge transport contributions in a single device.
  • The observed signal implies that orbital diffusion lengths in Ti are comparable to or longer than the smallest channel widths tested.
  • Nonlocal geometries become a viable probe for orbital Hall conductivity in materials where spin Hall signals are absent.

Where Pith is reading between the lines

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

  • The same width-scaling test could be applied to other light transition metals to map their orbital Hall angles without spin contamination.
  • If orbital currents prove long-lived, they might enable nonlocal orbital-based interconnects or logic elements.
  • A control experiment in a material known to lack orbital Hall response would cleanly isolate any remaining artifactual contributions.

Load-bearing premise

Finite-element simulations capture every possible Ohmic bypass path, and local resistivity fluctuations in the titanium film do not produce an unaccounted bypass signal at the widths used.

What would settle it

Repeat the nonlocal-resistance measurement at channel widths narrow enough that the simulated Ohmic bypass drops below the noise floor; if a finite signal remains, the orbital-transport interpretation is strengthened.

Figures

Figures reproduced from arXiv: 2605.00359 by Asahi Oe, Kazuya Ando, Keitaro Takashina, Mari Taniguchi, Naoki Yano, Shuto Kimura.

Figure 2
Figure 2. Figure 2: shows the measured nonlocal resistance Rnl as a function of the channel width W. Rnl remains finite over the entire measured range of W from 80 to 180 nm. An important contribution to the measured nonlocal re￾sistance Rnl is the Ohmic bypass signal R by nl . Assuming that the terminal widths are negligible compared with the channel length L, the bypass contribution is given by R by nl = 4 π Rsq exp  − πL … view at source ↗
Figure 1
Figure 1. Figure 1: FIG. 1. (a) Schematic of the nonlocal measurement geom view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Colored curves show simulated simulated bypass con view at source ↗
read the original abstract

We investigate nonlocal transport in single-layer Ti Hall bars to explore signatures of orbital-current transport driven by the orbital Hall effect. Despite the negligible spin Hall effect in Ti, we observe a finite nonlocal resistance in the single-layer Ti Hall bar and study its dependence on the central channel width. Finite-element simulations show that the measured signal contains a sizable Ohmic bypass contribution. However, the bypass contribution is strongly suppressed at small channel widths and cannot fully account for the observed nonlocal resistance even when variations in the Ti resistivity are taken into account. Our results therefore suggest an additional nonlocal contribution distinct from the Ohmic bypass background, which may be associated with orbital transport driven by the orbital Hall effect in Ti.

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

2 major / 3 minor

Summary. The manuscript reports measurements of nonlocal resistance in single-layer Ti Hall bars as a function of central channel width. Finite-element simulations indicate that a sizable Ohmic bypass contribution is present but strongly suppressed at small widths; even after including Ti resistivity variations, the simulations cannot account for the full measured signal. The authors conclude that the residual nonlocal resistance suggests an additional contribution possibly arising from orbital-current transport driven by the orbital Hall effect in Ti.

Significance. If the residual signal is robustly shown to exceed all Ohmic contributions, the work would provide useful experimental evidence for orbital Hall effect in a material with negligible spin Hall angle, supporting the broader development of orbitronics. The geometric-variation approach combined with simulation subtraction is a reasonable strategy for isolating non-Ohmic nonlocal signals.

major comments (2)
  1. [finite-element simulations and resistivity-variation analysis] The central claim that the measured nonlocal resistance exceeds all Ohmic contributions rests on the finite-element simulations fully capturing bypass effects even after resistivity variations are included. However, the manuscript provides insufficient detail on the spatial distribution, correlation length, or amplitude spectrum of the resistivity inhomogeneities that were modeled; without explicit tests of grain-boundary-like or fabrication-induced gradients whose length scales match the smallest channel widths, it remains possible that additional Ohmic bypass is unaccounted for.
  2. [results and comparison to simulations] Quantitative comparison between data and simulations is load-bearing for the subtraction step, yet the manuscript does not report error bars on the simulated nonlocal resistances arising from resistivity uncertainty or mesh convergence, nor does it show the raw data tables or fitting residuals that would allow independent verification of the claimed residual at small widths.
minor comments (3)
  1. The abstract and introduction would benefit from a short statement of the expected magnitude of the orbital Hall effect in Ti relative to the observed residual to help readers gauge the scale of the claimed effect.
  2. All figures showing width dependence should include both measured data points with error bars and the corresponding simulated Ohmic curves on the same plot for direct visual comparison.
  3. A table listing all simulation parameters (resistivity range, contact resistances, mesh density, etc.) would improve reproducibility.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive feedback and for acknowledging the potential importance of our work in providing evidence for the orbital Hall effect in Ti. We address the major comments point by point below and will make the necessary revisions to the manuscript.

read point-by-point responses

  1. Referee: The central claim that the measured nonlocal resistance exceeds all Ohmic contributions rests on the finite-element simulations fully capturing bypass effects even after resistivity variations are included. However, the manuscript provides insufficient detail on the spatial distribution, correlation length, or amplitude spectrum of the resistivity inhomogeneities that were modeled; without explicit tests of grain-boundary-like or fabrication-induced gradients whose length scales match the smallest channel widths, it remains possible that additional Ohmic bypass is unaccounted for.

    Authors: We agree that more detailed information on the resistivity inhomogeneity modeling would strengthen the manuscript. Our simulations incorporated resistivity variations based on experimental measurements of Ti film resistivity, modeled as random fluctuations. To fully address this point, we will expand the methods section with explicit details on the spatial distribution (using correlated random fields with correlation lengths on the order of grain sizes in Ti), the amplitude spectrum, and additional simulations testing grain-boundary-like patterns and fabrication-induced gradients scaled to the smallest channel widths. These new results will demonstrate that the Ohmic bypass remains insufficient to account for the observed signal, supporting our conclusion. revision: yes

  2. Referee: Quantitative comparison between data and simulations is load-bearing for the subtraction step, yet the manuscript does not report error bars on the simulated nonlocal resistances arising from resistivity uncertainty or mesh convergence, nor does it show the raw data tables or fitting residuals that would allow independent verification of the claimed residual at small widths.

    Authors: We acknowledge the need for greater transparency in the quantitative comparison. In the revised manuscript, we will add error bars to the simulated nonlocal resistance values, accounting for uncertainties in the input resistivity and confirming mesh convergence through systematic tests. Furthermore, we will include the raw data tables for both experimental and simulated nonlocal resistances, as well as the fitting residuals, in the supplementary material. This will enable independent verification and clearly illustrate the residual signal at small widths that exceeds the Ohmic contributions. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental comparison to independent simulations

full rationale

The paper is purely experimental, reporting measured nonlocal resistance in Ti Hall bars as a function of channel width and comparing it directly to separate finite-element simulations of Ohmic bypass (including resistivity variations). No derivation, ansatz, prediction, or uniqueness theorem is presented that reduces by construction to a parameter fitted from the same dataset or to a self-citation chain. The central suggestion of an additional orbital contribution rests on the empirical observation that simulations under-account for the signal at small widths, which is an external benchmark rather than a self-referential step. Any self-citations to prior orbital Hall work are not load-bearing for the reported data-simulation discrepancy.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No new theoretical entities or free parameters are introduced; the claim rests on standard assumptions of finite-element electrostatic modeling and the existence of an orbital Hall effect in Ti.

pith-pipeline@v0.9.0 · 5432 in / 1067 out tokens · 28798 ms · 2026-05-09T19:22:28.412810+00:00 · methodology

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Reference graph

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