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arxiv: 2605.06450 · v1 · submitted 2026-05-07 · ❄️ cond-mat.mes-hall

Recognition: unknown

Electrical Spin Pumping in Exchange-coupled Molecules

Paul Greule , Wantong Huang , Kwan Ho Au-Yeung , M\'at\'e Stark , Johannes Schwenk , Christoph S\"urgers , Wolfgang Wernsdorfer , Philip Willke
Authors on Pith no claims yet

Pith reviewed 2026-05-08 06:12 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall
keywords molecular spinsexchange interactionspin pumpingremote initializationquantum information processingscanning tunneling microscopyelectron spin resonance
0
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The pith

Exchange coupling between molecules allows all-electrical remote initialization of electron spins.

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

This paper establishes that electron spins in single molecules can be initialized remotely using only electrical means. In pairs of coupled molecules, a spin-polarized tunneling current through one sets the spin state of its neighbor via their exchange interaction. A reader would care because reliable initialization is a key requirement for using molecular spins as qubits in quantum information processing. The control depends on the current direction, its magnitude, and the strength of the coupling between the molecules. This method avoids the need for direct access to each spin individually.

Core claim

We demonstrate the remote, all-electrical initialization of the electron spin in single molecules using electron spin resonance scanning tunneling microscopy on coupled pairs of S=1/2 molecules. One molecule acts as a readout and pumping unit for the neighboring one, with the exchange interaction enabling angular momentum transfer. The remote spin state is controlled by the direction and magnitude of the spin-polarized tunneling current and the exchange coupling strength. This provides a general approach for remote spin initialization transferable to various spin-based quantum architectures.

What carries the argument

The exchange interaction between two S=1/2 molecules that transfers angular momentum from the spin-polarized current in the pumping molecule to the remote spin.

If this is right

  • The direction of the tunneling current determines the initialized spin state in the remote molecule.
  • Stronger exchange coupling enhances the efficiency of the angular momentum transfer.
  • This all-electrical method can be applied to other molecular or atomic spin systems for qubit initialization.
  • The technique allows control without optical or additional magnetic fields.

Where Pith is reading between the lines

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

  • If this mechanism generalizes, it could allow initialization of spins in larger molecular assemblies without individual addressing.
  • Combining this with existing STM capabilities might lead to on-surface assembly of spin networks with built-in initialization.
  • Variations in molecular separation could be used to tune the initialization rate in future devices.

Load-bearing premise

The observed control of the remote spin state arises from angular momentum transfer through the exchange interaction rather than from direct tunneling, heating, or measurement artifacts.

What would settle it

If the remote spin initialization disappears when the two molecules are decoupled by increasing their separation while maintaining the same tunneling current, that would indicate the exchange interaction is essential.

Figures

Figures reproduced from arXiv: 2605.06450 by Christoph S\"urgers, Johannes Schwenk, Kwan Ho Au-Yeung, M\'at\'e Stark, Paul Greule, Philip Willke, Wantong Huang, Wolfgang Wernsdorfer.

Figure 1
Figure 1. Figure 1: A). The thin MgO film serves as a decoupling layer to protect the single spin hosts from substrate electrons while maintaining sufficient conductivity for a finite tunneling current to probe the surface spins[21]. Using tip-assisted atom manipulation, single Fe atoms are combined with FePc molecules to form Fe-FePc complexes, where the additional Fe atom is positioned below one of the benzene rings of the … view at source ↗
Figure 2
Figure 2. Figure 2: Voltage dependence of the ESR spectra. Change in tunneling current ∆I as a function of radio-frequency shift δf = f − f0 for different VDC at constant conductance setpoint Gset [ESR conditions: same as in Fig. 1D]. The traces are normalized and vertically offset for clarity. In addition, they are centered at their resonance frequencies to compensate for the voltage induced frequency shift arising from spin… view at source ↗
Figure 3
Figure 3. Figure 3: Remote spin pumping in a molecule pair. (A) Spin excitation: Schematic of the tunnel junction illustrating the remote spin excitation towards |↓↓⟩ of the exchange coupled spins driven by the spin-polarized tunneling current for I < 0. (B) Energy level diagram of the coupled spin system. Flip-flop (FF) and remote scattering (RS) transitions that dominate for VDC < 0 are indicated by red arrows. ESR detectio… view at source ↗
Figure 4
Figure 4. Figure 4: Spin pumping for different exchange interaction strengths. view at source ↗
read the original abstract

Electron spins in single molecules are a promising platform for quantum information processing. However, their practical implementation as qubits requires reliable control at the single-entity level, including an efficient state initialization. Here, we demonstrate the remote, all-electrical initialization of the electron spin in single molecules: Using electron spin resonance scanning tunneling microscopy, we investigate coupled pairs of S=1/2 molecules (Fe-FePc), where one molecule serves as a readout and pumping unit for the neighboring one. We show that the exchange interaction between them enables angular momentum transfer, which allows for the control of the remote spin state via the direction and magnitude of the spin-polarized tunneling current and the exchange coupling strength. These results establish a general, all-electrical approach for remote spin initialization that is readily transferable to a wide range of spin-based quantum architectures.

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

0 major / 3 minor

Summary. The manuscript reports an experimental demonstration using electron spin resonance scanning tunneling microscopy (ESR-STM) on exchange-coupled pairs of S=1/2 Fe-FePc molecules. One molecule functions as a readout and pumping unit for the neighboring molecule, with the exchange interaction enabling angular momentum transfer that permits remote control of the spin state via the direction, magnitude, and strength of the spin-polarized tunneling current.

Significance. If the results hold, the work is significant for molecular quantum information platforms because it establishes a general, all-electrical route to remote spin initialization that relies on a falsifiable signature (dependence on current polarity, magnitude, and coupling strength) rather than optical or magnetic fields. The experimental approach is readily transferable to other exchange-coupled spin architectures and supplies a concrete mechanism for angular-momentum transfer that can be tested quantitatively.

minor comments (3)
  1. The abstract states the central claim clearly but would benefit from a single sentence noting the quantitative dependence on exchange coupling strength to preview the falsifiable signature.
  2. In the methods or experimental section, the description of how the remote spin state is read out should explicitly reference the ESR resonance condition used for the readout molecule to avoid ambiguity in the pumping-versus-readout assignment.
  3. Figure captions (where present) should include the specific bias voltages and current ranges corresponding to the spin-polarized pumping regime so that readers can directly map the data to the claimed control parameters.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive assessment of our manuscript on electrical spin pumping in exchange-coupled Fe-FePc molecules. We appreciate the recognition of the significance for molecular quantum information platforms and the recommendation for minor revision. No specific major comments were raised in the report.

Circularity Check

0 steps flagged

No significant circularity; experimental claims rest on direct measurements

full rationale

The paper presents experimental results from ESR-STM on Fe-FePc molecular pairs, demonstrating remote spin initialization via observed changes in spectra as a function of tunneling current direction, magnitude, and exchange coupling strength. No derivation chain, equations, or fitted parameters are invoked to 'predict' the central observations; the angular-momentum-transfer interpretation is supported by falsifiable signatures in the data rather than by construction from inputs. Self-citations, if present, are not load-bearing for the core claim, and the work is self-contained against external benchmarks such as measured spectra and current dependence.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work is experimental and relies on standard condensed-matter physics; no free parameters or invented entities are introduced in the abstract.

axioms (1)
  • standard math Standard quantum mechanics governs electron spins and exchange interactions in molecular systems
    Invoked implicitly when attributing angular momentum transfer to exchange coupling.

pith-pipeline@v0.9.0 · 5466 in / 1146 out tokens · 46528 ms · 2026-05-08T06:12:14.033538+00:00 · methodology

discussion (0)

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Reference graph

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