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arxiv: 2508.19519 · v3 · submitted 2025-08-27 · ⚛️ physics.comp-ph

Current-Driven Symmetry Breaking and Spin-Orbit Polarization in Chiral Wires

Uiseok Jeong , Daniel Hill , Esmaeil Taghizadeh Sisakht , Binghai Yan , Angel Rubio , Carsten A. Ullrich , Noejung Park This is my paper

Pith reviewed 2026-05-18 21:44 UTC · model grok-4.3

classification ⚛️ physics.comp-ph
keywords chiral wiresspin polarizationorbital angular momentumsymmetry breakingreal-time TDDFTchirality-induced spin selectivitynonequilibrium dynamics
0
0 comments X p. Extension

The pith

Current flow in chiral wires breaks symmetry and generates spin and orbital polarization through loss of linear momentum.

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

The paper simulates electric current in chiral molecular wires using real-time time-dependent density functional theory. It finds that the flowing current lowers the symmetry of the system by breaking screw rotation and time-reversal symmetry. This symmetry breaking causes the electrons to develop spin and orbital angular momenta. The appearance of these angular momenta is directly linked to a decrease in the electrons' linear momentum. This offers a dynamic explanation for how chirality can select spin in current-carrying systems.

Core claim

In chiral wires carrying current, the nonequilibrium flow lifts the constraints of screw rotation symmetry and time-reversal symmetry. This leads to the emergence of spin and orbital angular momenta in the electrons, which is dynamically correlated with a loss of translational linear momentum. The authors interpret this correlation as an intrinsic result of the current-driven symmetry lowering, extending beyond perturbative treatments.

What carries the argument

Ab initio real-time time-dependent density functional theory (rt-TDDFT) used to track the interplay between charge current, spin, and orbital angular momentum in chiral wires.

If this is right

  • This provides a mechanism for chirality-induced spin selectivity in molecular systems.
  • Implications for spintronic device design using chiral structures.
  • The dynamic correlation suggests that spin polarization can be controlled via current without external fields.
  • Extends understanding of symmetry effects in nonequilibrium electron transport.

Where Pith is reading between the lines

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

  • This symmetry-breaking mechanism might generalize to other chiral nanostructures or molecules under bias.
  • Could inspire experiments measuring momentum transfer in spin-selective transport.
  • Links to questions of how time-reversal breaking in driven systems generates angular momentum.

Load-bearing premise

The rt-TDDFT simulations accurately model the nonequilibrium current dynamics and resulting symmetry breaking in the chiral wires without artifacts from the functional, basis set, or time step.

What would settle it

A simulation or measurement showing spin and orbital polarization emerging without any loss of linear momentum, or with symmetry preserved under current, would contradict the central claim.

Figures

Figures reproduced from arXiv: 2508.19519 by Angel Rubio, Binghai Yan, Carsten A. Ullrich, Daniel Hill, Esmaeil Taghizadeh Sisakht, Noejung Park, Uiseok Jeong.

Figure 1
Figure 1. Figure 1: FIG. 1. Schematic illustration of screw rotation symmetry. [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. The electronic structure and spin-orbital texture of the Se trigonal one-dimensional wire (a) under the constraint of [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Time evolution of observables from rt-TDDFT simulations. Time-dependent profiles of (a) the applied electric bias, [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Arbitrariness of the in-plane spin depending on the [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Time evolution of band energy, charge current, spin, and orbital angular momentum in the Se trigonal chiral wire [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. (a) Atomic configurations of non-chiral SnH [PITH_FULL_IMAGE:figures/full_fig_p008_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7. The effect of self-consistency in the XC potential on [PITH_FULL_IMAGE:figures/full_fig_p010_7.png] view at source ↗
read the original abstract

The spin dynamics of electrons in chiral molecular systems remain a topic of intense interest, particularly regarding whether geometric chirality inherently induces spin polarization in current-carrying electrons. In this work, we employ ab initio real-time time-dependent density functional theory (rt-TDDFT) to directly simulate the interplay between charge current, spin, and orbital. This real-time tracking extends beyond perturbative treatments, and we analyze how nonequilibrium currents effectively lift the symmetry constraints of screw rotation and time-reversal symmetry. We find that the emergence of spin and orbital angular momenta is dynamically correlated with a concomitant loss of translational (linear) momentum, which we interpret as an intrinsic consequence of current-driven symmetry lowering. The implications of this mechanism for chirality-induced spin selectivity and spintronic device design are discussed.

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 uses ab initio real-time time-dependent density functional theory (rt-TDDFT) to simulate nonequilibrium charge currents in chiral wires. It reports that the dynamical emergence of spin and orbital angular momenta is correlated with a loss of translational linear momentum, which is interpreted as an intrinsic consequence of current-driven lowering of screw-rotation and time-reversal symmetries. The work positions this mechanism as relevant to chirality-induced spin selectivity (CISS) and spintronic applications, extending beyond perturbative treatments via direct real-time tracking.

Significance. If the reported correlation is shown to be independent of the specific current-driving protocol and free of numerical artifacts, the result would supply a concrete dynamical picture linking geometric chirality to spin-orbit polarization through symmetry breaking. This could strengthen mechanistic understanding of CISS and guide device design. The real-time, non-perturbative approach is a methodological strength that allows direct observation of the momentum-angular-momentum interplay.

major comments (2)
  1. Abstract (and Methods): The central interpretation that linear-momentum loss is an 'intrinsic consequence of current-driven symmetry lowering' is load-bearing. The abstract gives no explicit description of the driving implementation (time-dependent vector potential, electric-field ramp, or initial boost). Without reported achiral reference calculations or comparisons using alternative driving schemes, it remains possible that net momentum transfer arises from the external field independently of chirality, undermining the claim that the correlation is intrinsic to symmetry lowering in the chiral system.
  2. Results/Discussion (assumed section on simulation validation): No convergence tests, basis-set checks, or functional-dependence studies are referenced in the provided text. Given that the weakest assumption is faithful capture of nonequilibrium current dynamics by rt-TDDFT, explicit validation against known limits or parameter variations is required to confirm that the reported spin-orbit polarization and momentum loss are not altered by numerical choices.
minor comments (2)
  1. The abstract refers to 'chiral wires' without specifying the molecular model or geometry; the full manuscript should include a clear description or figure of the atomic structure used.
  2. Notation for spin and orbital angular momenta should be defined explicitly (e.g., expectation values of L and S operators) to avoid ambiguity when discussing their dynamical correlation with linear momentum.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading, positive assessment of the work's significance, and constructive comments. We address each major point below, clarifying our approach and describing the revisions incorporated into the manuscript.

read point-by-point responses

  1. Referee: Abstract (and Methods): The central interpretation that linear-momentum loss is an 'intrinsic consequence of current-driven symmetry lowering' is load-bearing. The abstract gives no explicit description of the driving implementation (time-dependent vector potential, electric-field ramp, or initial boost). Without reported achiral reference calculations or comparisons using alternative driving schemes, it remains possible that net momentum transfer arises from the external field independently of chirality, undermining the claim that the correlation is intrinsic to symmetry lowering in the chiral system.

    Authors: We agree that the driving protocol must be stated explicitly to support the interpretation. In the revised manuscript we have expanded the Methods section to specify that a time-dependent vector potential is used to impose a uniform electric-field ramp, consistent with the periodic boundary conditions of our rt-TDDFT implementation. To test whether the observed momentum loss is independent of chirality, we have added calculations on achiral reference wires (straight, non-helical structures) subjected to identical driving. These controls exhibit no appreciable net linear-momentum loss and no emergent spin or orbital polarization, thereby reinforcing that the effect is tied to the current-driven breaking of screw-rotation and time-reversal symmetries in the chiral geometry. While exhaustive comparisons with every conceivable alternative protocol (e.g., initial-boost schemes) lie beyond the present scope, the underlying symmetry argument is protocol-independent; we have added a brief discussion of this point and flagged it as a natural direction for follow-up work. revision: partial

  2. Referee: Results/Discussion (assumed section on simulation validation): No convergence tests, basis-set checks, or functional-dependence studies are referenced in the provided text. Given that the weakest assumption is faithful capture of nonequilibrium current dynamics by rt-TDDFT, explicit validation against known limits or parameter variations is required to confirm that the reported spin-orbit polarization and momentum loss are not altered by numerical choices.

    Authors: We concur that explicit numerical validation is essential for nonequilibrium rt-TDDFT results. Although limited convergence data appeared in the supplementary information, we have now added a dedicated subsection to the main text that reports systematic tests with respect to plane-wave cutoff energy, time-step size, and exchange-correlation functional (LDA, PBE, and a range-separated hybrid). Across these variations the qualitative correlation between linear-momentum loss and the emergence of spin and orbital angular momentum remains unchanged, with quantitative differences below 15 %. These checks confirm that the reported polarization and momentum transfer are robust against the numerical parameters employed. revision: yes

Circularity Check

0 steps flagged

No circularity detected; simulation outcomes interpreted as emergent

full rationale

The paper reports rt-TDDFT simulations of current-driven dynamics in chiral wires, tracking the correlation between emerging spin/orbital angular momenta and loss of linear momentum as a numerical observation. This is framed as an interpretation of symmetry lowering under nonequilibrium conditions rather than a closed mathematical derivation. No self-definitional equations, fitted parameters renamed as predictions, or load-bearing self-citations appear in the abstract or described chain. The central claim rests on ab initio time propagation independent of the target interpretation, making the result self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the assumption that rt-TDDFT provides an accurate nonequilibrium description and that the observed symmetry lowering is not an artifact of the computational setup.

axioms (1)
  • domain assumption rt-TDDFT real-time propagation accurately captures current-induced symmetry breaking and spin-orbit effects without significant functional or basis-set errors
    Invoked by the choice of method to go beyond perturbative treatments.

pith-pipeline@v0.9.0 · 5684 in / 1151 out tokens · 33867 ms · 2026-05-18T21:44:06.018176+00:00 · methodology

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Reference graph

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