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arxiv: 2602.08766 · v3 · pith:3RRVCPHGnew · submitted 2026-02-09 · ❄️ cond-mat.mes-hall · cond-mat.supr-con

Josephson diode and spin-valve effects on the surface of altermagnet CrSb

V.D. Esin , D.Yu. Kazmin , Yu.S. Barash , A.V. Timonina , N.N. Kolesnikov , E.V. Deviatov This is my paper

Pith reviewed 2026-05-22 10:58 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall cond-mat.supr-con
keywords altermagnetCrSbJosephson diodespin valvetopological surface statesFFLO pairingsuperconducting proximitymagnetic field dependence
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The pith

Altermagnet CrSb produces Josephson diode and spin-valve effects in indium junctions through its spin-polarized topological surface states and bulk band splitting.

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

The paper experimentally shows direction-dependent critical currents and mirrored resistance curves in In-CrSb and In-CrSb-In devices, establishing Josephson diode and spin-valve behaviors. These appear under applied magnetic fields and are linked to the altermagnetic spin splitting of CrSb bulk bands together with its spin-polarized topological surface states. The single-interface data further display oscillating superconducting gaps resembling Fulde-Ferrell-Larkin-Ovchinnikov pairing, which fits the finite-momentum requirements for the diode effect. A sympathetic reader would care because this points to a route for superconducting spintronic elements that avoid net magnetization.

Core claim

In In-CrSb-In double junctions the differential resistance curves mirror under opposite magnetic-field sweep directions, characteristic of a Josephson spin valve, while direct critical-current measurements reveal a Josephson diode effect; single In-CrSb interfaces show magnetic-field oscillations of the gap that match FFLO finite-momentum pairing; both phenomena are produced by the combination of spin-polarized topological surface states and altermagnetic bulk spin splitting in CrSb.

What carries the argument

Joint action of spin-polarized topological surface states and altermagnetic spin splitting of the bulk bands in CrSb

If this is right

  • Altermagnets can replace ferromagnets in superconducting circuits while retaining spin-valve and diode functionality.
  • Finite-momentum Cooper pairing becomes accessible at the surface of an altermagnet in proximity to a conventional superconductor.
  • Josephson devices can be engineered without external magnetic elements by exploiting intrinsic altermagnetic splitting.
  • The observed effects remain compatible with zero net magnetization, reducing stray-field interference in integrated circuits.

Where Pith is reading between the lines

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

  • Similar diode and valve behaviors may appear in other altermagnets once their surface states are brought into contact with superconductors.
  • The FFLO-compatible oscillations suggest a route to tunable finite-momentum pairing that could be tested by varying the junction transparency.
  • Device architectures that combine altermagnetic flakes with multiple superconducting leads could enable non-reciprocal transport without external fields.

Load-bearing premise

The diode and spin-valve signals arise from the altermagnetic order and topological surface states of CrSb rather than from conventional ferromagnetic domains, interface disorder, or magnetic impurities.

What would settle it

Absence of direction-dependent critical currents and mirrored dV/dI curves in otherwise identical junctions made with non-altermagnetic crystals of similar composition or with CrSb samples in which the altermagnetic order has been suppressed.

read the original abstract

We experimentally investigate charge transport in In-CrSb and In-CrSb-In proximity devices, which are formed as junctions between superconducting indium leads and thick single crystal flakes of altermagnet CrSb. For double In-CrSb-In junctions, $dV/dI(B)$ curves are mirrored in respect to zero field for two magnetic field sweep directions, which is characteristic behavior of a Josephson spin valve. Also, we demonstrate Josephson diode effect by direct measurement of the critical current for two opposite directions in external magnetic field. We interpret these observations as a joint effect of the spin-polarized topological surface states and the altermagnetic spin splitting of the bulk bands in CrSb. For a single In-CrSb interface, the superconducting gap oscillates in magnetic field for both field orientations, which strongly resembles the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) behavior. FFLO is based on finite-momentum Cooper pairing, therefore, it is fully compatible with the requirements for the Josephson diode effect.

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 / 1 minor

Summary. The manuscript reports experimental charge transport measurements in In-CrSb and In-CrSb-In proximity junctions fabricated on thick single-crystal flakes of the altermagnet CrSb. In double-junction devices, dV/dI(B) curves are mirrored for opposite magnetic-field sweep directions, taken as evidence of Josephson spin-valve behavior; direction-dependent critical currents demonstrate the Josephson diode effect. In single In-CrSb interfaces the superconducting gap oscillates with applied field for both orientations, resembling Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing. These signatures are interpreted as arising from the joint action of spin-polarized topological surface states and altermagnetic bulk spin splitting.

Significance. If the material-specific attribution is secured, the work would establish altermagnetic CrSb as a platform for realizing Josephson diodes and spin valves, extending superconducting spintronics beyond conventional ferromagnets. The experimental demonstration of mirrored field-sweep behavior and direction-dependent Ic, together with FFLO-like gap oscillations, is a concrete observation that could stimulate further theory and device work. The impact remains conditional on distinguishing the proposed altermagnetic mechanism from conventional magnetic explanations.

major comments (2)
  1. [Abstract] Abstract: The central claim that the diode and spin-valve effects originate specifically from altermagnetic spin splitting combined with topological surface states rests on an interpretive step that excludes conventional alternatives (residual net magnetization, ferromagnetic domains, or interface impurities). No magnetization data, temperature-dependent susceptibility, or control measurements on non-altermagnetic analogs are referenced to support this attribution.
  2. [Results] Results (qualitative signatures): The mirrored dV/dI(B) curves and direction-dependent critical currents are presented without quantitative error bars, statistical measures of reproducibility, or explicit comparison to expected field scales set by the altermagnetic exchange or surface-state spin polarization; this weakens the ability to rule out extrinsic mechanisms.
minor comments (1)
  1. [Abstract] The abstract would be strengthened by a short clause indicating the typical flake thickness and junction geometry used in the devices.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the constructive comments provided. We respond to each major comment below, indicating where revisions will be made to address the concerns.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The central claim that the diode and spin-valve effects originate specifically from altermagnetic spin splitting combined with topological surface states rests on an interpretive step that excludes conventional alternatives (residual net magnetization, ferromagnetic domains, or interface impurities). No magnetization data, temperature-dependent susceptibility, or control measurements on non-altermagnetic analogs are referenced to support this attribution.

    Authors: The attribution is based on the known altermagnetic properties of CrSb, which features spin-split bands with zero net magnetization, as established in prior theoretical and experimental works. We will update the abstract to explicitly reference these properties and include citations to magnetization studies confirming the absence of net moment in CrSb. We disagree that conventional alternatives are not excluded, as the mirrored sweep behavior and FFLO-like oscillations are not typical for standard ferromagnetic interfaces. However, to further support, we will add a section discussing why residual magnetization or domains would not produce the observed effects. Control measurements on non-altermagnetic materials are not included as they are not directly comparable without matching the topological surface states present in CrSb. revision: partial

  2. Referee: [Results] Results (qualitative signatures): The mirrored dV/dI(B) curves and direction-dependent critical currents are presented without quantitative error bars, statistical measures of reproducibility, or explicit comparison to expected field scales set by the altermagnetic exchange or surface-state spin polarization; this weakens the ability to rule out extrinsic mechanisms.

    Authors: We will revise the results section to include error bars on the relevant data points, provide information on the number of devices measured and reproducibility, and add a quantitative comparison of the magnetic field values at which the effects occur to the expected scales from altermagnetism (typically on the order of the exchange field in CrSb) and surface state polarization. This will strengthen the case against extrinsic mechanisms. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental observations with qualitative interpretation

full rationale

The manuscript reports transport measurements on In-CrSb proximity devices and interprets the mirrored dV/dI(B) curves and direction-dependent critical currents as signatures of spin-polarized topological surface states combined with altermagnetic bulk splitting. No equations, fitted parameters, or derivation chain appear in the provided text; the central claims rest on direct comparison of observed behaviors (Josephson spin-valve mirroring, diode effect, FFLO-like gap oscillations) to expected qualitative features rather than any self-referential reduction or self-citation load-bearing step. The analysis is therefore self-contained against external benchmarks and receives the default non-circularity finding.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

No free parameters or invented entities appear; the central interpretation rests on standard assumptions of proximity-induced superconductivity and the established altermagnetic band structure of CrSb.

axioms (2)
  • domain assumption CrSb exhibits altermagnetic spin splitting of bulk bands and spin-polarized topological surface states
    Invoked in the final interpretive sentence of the abstract to link observations to material properties.
  • domain assumption Observed gap oscillations indicate finite-momentum Cooper pairing compatible with Josephson diode requirements
    Stated directly in the abstract as the basis for compatibility with diode effect.

pith-pipeline@v0.9.0 · 5746 in / 1335 out tokens · 25378 ms · 2026-05-22T10:58:42.296813+00:00 · methodology

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Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Perfect spin nonreciprocity in gated superconducting altermagnetic heterostructures

    cond-mat.supr-con 2026-04 unverdicted novelty 5.0

    Gating a finite normal region between a superconducting altermagnet and a metallic reservoir produces perfect nonreciprocal spin and charge currents with tunable polarity via gate voltage and region length.