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arxiv: 2312.04650 · v1 · pith:FKV5KDM5new · submitted 2023-12-07 · ❄️ cond-mat.supr-con

Field-free Josephson diode with controllable efficiency using magnetic tunnel barrier

Pramod K. Sharma , Sagnik Banerjee , Biswajit Dutta , Vansh Singhal , Pushpak Banerjee , Hridis K. Pal , Avradeep Pal This is my paper

Pith reviewed 2026-05-24 05:35 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con
keywords Josephson diodezero-field diode effectmagnetic tunnel barrierNbN/GdN/NbN junctionsuperconducting rectificationmicromagnetic structureswitching current asymmetry
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The pith

A magnetic tunnel barrier in asymmetric Josephson junctions produces a robust zero-field diode effect whose efficiency reaches 40 percent when the barrier's micromagnetic structure is modified.

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

The paper establishes that an asymmetric Josephson junction with a magnetic weak link can generate diode-like non-reciprocal switching currents without any applied magnetic field. The approach is realized in sputter-deposited NbN/GdN/NbN tri-layer mesa junctions, where the GdN barrier supplies the necessary asymmetry. Efficiency is shown to increase to 40 percent through controlled changes to the barrier's micromagnetic configuration, while the effect persists from millikelvin temperatures up to at least 4.2 K and supports operation near 28 GHz.

Core claim

An asymmetric Josephson junction that incorporates a magnetic weak link exhibits a zero-field diode effect in its switching current; the efficiency of this effect can be increased up to 40 percent by altering the micromagnetic structure of the barrier, as demonstrated in fabricated long NbN/GdN/NbN junctions in cross geometry.

What carries the argument

The micromagnetic configuration of the GdN magnetic barrier, which breaks reciprocity in the Josephson critical current without external fields.

If this is right

  • The diode maintains high efficiency from the lowest accessible temperatures up to at least 4.2 K.
  • Efficiency can be raised to 40 percent by deliberate modification of the barrier's micromagnetic structure.
  • The junctions operate at frequencies approaching 28 GHz.
  • The fabrication uses standard sputter deposition and mesa patterning, indicating a scalable route to field-free Josephson diodes.

Where Pith is reading between the lines

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

  • Absence of external magnets could simplify integration of these diodes into dense superconducting circuits.
  • The same magnetic-barrier approach may be transferable to other material combinations or junction geometries that require non-reciprocal transport.
  • Voltage-tunable or current-tunable control of the micromagnetic state would allow in-situ adjustment of diode polarity or efficiency after fabrication.

Load-bearing premise

The observed difference between positive and negative switching currents is caused by the micromagnetic state of the GdN layer rather than by geometric asymmetry from fabrication or by trapped magnetic flux.

What would settle it

Fabrication and measurement of otherwise identical NbN junctions that lack the GdN magnetic layer and show equal positive and negative switching currents would falsify the claim that the magnetic barrier produces the diode effect.

Figures

Figures reproduced from arXiv: 2312.04650 by Avradeep Pal, Biswajit Dutta, Hridis K. Pal, Pramod K. Sharma, Pushpak Banerjee, Sagnik Banerjee, Vansh Singhal.

Figure 1
Figure 1. Figure 1: FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
read the original abstract

Josephson diodes (JDs) offer a promising route towards realizing dissipation-less rectification at low temperatures. To be practically viable, a JD must operate at zero magnetic fields, exhibit high operating frequencies and efficiency, and possess tunability and scalability. In this study, we propose and experimentally demonstrate a straightforward mechanism that encompasses all these crucial features. Our approach involves utilizing an asymmetric Josephson junction with a magnetic weak link to attain a diode effect in the switching current. We substantiate this concept experimentally through the fabrication of mesa-type sputter-deposited tri-layered ferromagnetic long NbN/GdN/NbN Josephson junctions (JJs) in cross geometry. A robust zero-field diode effect is observed with an efficiency boost of up to 40% achievable through modification of the micromagnetic structure of the barrier. Notably, these diodes maintain high efficiency across a wide temperature range, from the lowest temperatures up to at least 4.2K, and exhibit an operating frequency of nearly 28GHz.

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 / 2 minor

Summary. The manuscript experimentally demonstrates a field-free Josephson diode effect in sputter-deposited NbN/GdN/NbN tri-layer junctions fabricated in cross geometry. It reports a robust zero-field switching-current asymmetry whose efficiency can be boosted up to 40% by modifying the micromagnetic structure of the GdN barrier; the devices are stated to retain high efficiency from base temperature to at least 4.2 K and to operate at frequencies approaching 28 GHz.

Significance. If the micromagnetic origin of the asymmetry is confirmed, the work supplies a scalable, tunable, zero-field Josephson diode that simultaneously satisfies the practical requirements of high efficiency, wide temperature range, and GHz-range operation. The approach of using a magnetic tunnel barrier for both the diode effect and its controllability would constitute a clear advance over existing field-dependent or geometrically asymmetric designs.

major comments (2)
  1. [Description of the tri-layered ferromagnetic long junctions and associated results] The central claim that the observed switching-current asymmetry originates from the micromagnetic configuration of the GdN barrier (rather than from mesa geometry or trapped flux) is load-bearing for the entire interpretation. The manuscript describes the tri-layered long junctions and reports efficiency tuning via micromagnetic modification, yet presents no data from control devices (NbN/NbN or NbN/non-magnetic-barrier/NbN junctions fabricated in identical cross geometry). Without these controls the attribution remains an untested assumption.
  2. [Results on efficiency tuning] The reported efficiency boost of up to 40% is stated to arise from deliberate modification of the barrier's micromagnetic structure. No quantitative micromagnetic characterization (e.g., MFM images, hysteresis loops, or micromagnetic simulations correlated with the transport data) is provided to establish that the efficiency change tracks the intended magnetic reconfiguration rather than other junction parameters.
minor comments (2)
  1. [Abstract and results] The operating frequency of nearly 28 GHz is quoted without an accompanying measurement protocol or reference to the specific figure or supplementary section that reports the data.
  2. [Results] Error bars, number of devices measured, and statistics on the efficiency values are not mentioned in the abstract or the summary of results.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their thorough review and constructive feedback. We address each major comment below and outline the revisions we plan to make to strengthen the manuscript.

read point-by-point responses

  1. Referee: The central claim that the observed switching-current asymmetry originates from the micromagnetic configuration of the GdN barrier (rather than from mesa geometry or trapped flux) is load-bearing for the entire interpretation. The manuscript describes the tri-layered long junctions and reports efficiency tuning via micromagnetic modification, yet presents no data from control devices (NbN/NbN or NbN/non-magnetic-barrier/NbN junctions fabricated in identical cross geometry). Without these controls the attribution remains an untested assumption.

    Authors: We agree that dedicated control devices would provide stronger evidence. However, the cross geometry is symmetric by design, and the zero-field diode effect together with its tunability via magnetic protocols is observed specifically with the GdN barrier; literature on non-magnetic junctions in comparable geometries shows no such asymmetry. The temperature range up to 4.2 K and near-28 GHz operation are also consistent with a magnetic origin. In revision we will add an explicit symmetry argument section plus references to prior non-magnetic control-like results. revision: partial

  2. Referee: The reported efficiency boost of up to 40% is stated to arise from deliberate modification of the barrier's micromagnetic structure. No quantitative micromagnetic characterization (e.g., MFM images, hysteresis loops, or micromagnetic simulations correlated with the transport data) is provided to establish that the efficiency change tracks the intended magnetic reconfiguration rather than other junction parameters.

    Authors: The efficiency changes are shown to be reproducible and to follow specific magnetic-field or current protocols applied to the GdN layer, whose ferromagnetic domain structure is known to be reconfigurable. While the present manuscript does not include direct micromagnetic imaging, the transport data correlate with magnetic history. We will add micromagnetic simulations in the revised manuscript that quantitatively connect the observed efficiency variations to changes in the GdN micromagnetic configuration. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental measurements with no derivation chain

full rationale

The manuscript is an experimental report on fabricated NbN/GdN/NbN Josephson junctions. The central results (zero-field diode effect, efficiency values up to 40%, temperature and frequency performance) are obtained by direct measurement of switching currents in the devices. No equations, fitted parameters, or theoretical derivations are invoked that could reduce to self-definition or self-citation. The interpretation that the asymmetry originates from the GdN micromagnetic structure is an unverified assumption (as noted by the skeptic), but this is a question of experimental controls, not a circular reduction in any claimed derivation. The work is therefore self-contained against external benchmarks with score 0.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No free parameters, axioms, or invented entities are introduced; the result is an experimental measurement of fabricated devices.

pith-pipeline@v0.9.0 · 5728 in / 1233 out tokens · 16935 ms · 2026-05-24T05:35:58.695616+00:00 · methodology

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Reference graph

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