arxiv: 2605.11113 · v1 · submitted 2026-05-11 · ❄️ cond-mat.mes-hall · cond-mat.other

Recognition: 1 theorem link

· Lean Theorem

Photon Momentum Enabled Symmetry Breaking and Nonlinear Photocurrents in the Centrosymmetric Dirac Semimetal PdTe

Sambhu G Nath , Subhadip Manna , R K Gopal , Chiranjib Mitra

Authors on Pith no claims yet

Pith reviewed 2026-05-13 02:28 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall cond-mat.other

keywords photon momentumsymmetry breakingnonlinear photocurrentsDirac semimetalPdTecentrosymmetricCPGEquantum geometry

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The pith

Finite photon momentum breaks inversion symmetry in centrosymmetric PdTe, enabling bulk nonlinear photocurrents normally forbidden by symmetry.

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

In centrosymmetric Dirac semimetals such as PdTe, time-reversal and inversion symmetries normally forbid second-order nonlinear photocurrents. The paper shows that the small but finite momentum carried by incident photons supplies a directional axis that dynamically reduces the effective symmetry. Polarization-resolved measurements separate the circular photogalvanic effect, geometric shift currents, and photon-drag contributions. Thickness-dependent data reveal that the helicity-dependent photocurrent component grows with film thickness, demonstrating that the response is a bulk phenomenon enabled by photon momentum rather than a surface artifact.

Core claim

Finite photon momentum transfer acts as a dynamic symmetry breaking mechanism in PdTe, enabling nonlinear optical responses that are nominally forbidden in the centrosymmetric bulk. Through polarization sensitive measurements, distinct contributions from the circular photogalvanic effect, geometric shift currents, and photon drag processes are resolved. The helicity dependent photocurrent vanishes at normal incidence, reverses sign with the angle of incidence, and scales with film thickness, establishing a robust bulk contribution that allows optical access to interband quantum geometry.

What carries the argument

Photon momentum transfer acting as a dynamic inversion symmetry breaker that couples incident light to spin-polarized states and quantum geometric tensors.

If this is right

Helicity-dependent current vanishes at normal incidence and reverses with angle of incidence.
Distinct CPGE, geometric shift-current, and photon-drag terms can be separated by polarization and incidence angle.
Thickness scaling establishes that the nonlinear response is a bulk effect enabled by photon momentum.
Optical excitation can dynamically lower symmetry to probe quantum geometric tensors in high-symmetry topological materials.

Where Pith is reading between the lines

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

The same photon-momentum mechanism could be tested in other centrosymmetric topological semimetals to determine how generally it enables forbidden nonlinear responses.
It opens the possibility of momentum-selective optical control of nonequilibrium currents without requiring static symmetry lowering by strain or surfaces.
Experiments that vary photon energy while keeping momentum transfer fixed could isolate the geometric versus drag contributions.

Load-bearing premise

The observed scaling of the helicity-dependent photocurrent with film thickness arises solely from bulk photon-momentum symmetry breaking and not from thickness-dependent surface states, strain, or scattering.

What would settle it

If the helicity-dependent photocurrent component fails to increase proportionally with film thickness in thicker samples or remains unchanged when surface-state contributions are independently suppressed, the bulk photon-momentum mechanism would be ruled out.

Figures

Figures reproduced from arXiv: 2605.11113 by Chiranjib Mitra, R K Gopal, Sambhu G Nath, Subhadip Manna.

**Figure 2.** Figure 2: FIG. 2. (a,b) Photocurrent density [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗

**Figure 3.** Figure 3: FIG. 3. Angle of incidence ( [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

**Figure 4.** Figure 4: FIG. 4. (a) Polarization dependent modulation of the photocurrent measured at different values of [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗

**Figure 5.** Figure 5: FIG. 5. (a) Photocurrent [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗

**Figure 6.** Figure 6: FIG. 6. (a,b) Photocurrent density [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗

**Figure 7.** Figure 7: FIG. 7. (a) Dependence of the fitting parameters [PITH_FULL_IMAGE:figures/full_fig_p008_7.png] view at source ↗

read the original abstract

In centrosymmetric Dirac semimetals, second order nonlinear photocurrents are forbidden by the coexistence of time-reversal and inversion symmetries. Here, we demonstrate that finite photon momentum transfer acts as a dynamic symmetry breaking mechanism in PdTe, enabling nonlinear optical responses that are nominally forbidden in the centrosymmetric bulk. Through polarization sensitive measurements, we resolve distinct contributions from the circular photogalvanic effect (CPGE), geometric shift currents, and photon drag mediated processes. We show that the helicity dependent current vanishes at normal incidence and reverses sign with the angle of incidence, reflecting the coupling between photons and spin polarized surface states. Crucially, thickness dependent analysis reveals that the helicity dependent photocurrent component C scales with film thickness, establishing a robust bulk contribution enabled by momentum transfer. This confirms that incident photons provide the directional axis required to probe interband quantum geometry, rather than the response originating solely from surface states or strain. Our results demonstrate that optical excitation can dynamically reduce the effective symmetry of the system, enabling access to quantum geometric tensors and establishing PdTe as a promising platform for exploring nonequilibrium dynamics governed by photon momentum in high symmetry topological materials.

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.

Desk Editor's Note private letter to a colleague

Photon momentum lets them pull forbidden nonlinear photocurrents out of centrosymmetric PdTe, with angle reversal and thickness scaling as the main evidence.

read the letter

The core result is that oblique light incidence supplies a small photon momentum q that dynamically breaks inversion symmetry in PdTe, allowing a helicity-dependent photocurrent that should be forbidden in the bulk. The current drops to zero at normal incidence and reverses sign when the angle flips, which lines up with the expected coupling to spin-polarized states. They also separate the circular photogalvanic, shift-current, and photon-drag pieces through polarization scans, and the helicity term grows with film thickness, which they take as the signature that the response is bulk rather than surface-only. That combination is the actual new piece: a practical way to access quantum-geometry effects in a high-symmetry Dirac semimetal without static symmetry breaking. The angle dependence looks clean and reproducible from the description. The thickness scaling is the part that feels soft. Changing thickness in epitaxial films also relaxes strain, alters surface-state density, and changes optical penetration, any of which can produce a roughly linear trend in photocurrent without needing photon-momentum symmetry breaking. The abstract does not show raw traces, error bars, or the exact fitting procedure, so it is hard to judge how well those alternatives were excluded. If the full paper has good controls on strain and surface preparation, the claim strengthens; otherwise the bulk assignment stays under-constrained. This is worth sending to referees. The experimental signatures are concrete enough that specialists in topological optoelectronics will want to see the data and the analysis in detail, even if the interpretation needs tightening.

Referee Report

2 major / 2 minor

Summary. The manuscript reports on nonlinear photocurrents in the centrosymmetric Dirac semimetal PdTe. The central claim is that finite photon momentum transfer serves as a dynamic symmetry-breaking mechanism, enabling second-order nonlinear optical responses such as the circular photogalvanic effect (CPGE), geometric shift currents, and photon drag processes that are forbidden by the coexistence of time-reversal and inversion symmetries in the bulk. Polarization-sensitive measurements reveal that the helicity-dependent photocurrent vanishes at normal incidence and reverses sign with the angle of incidence. Thickness-dependent measurements show that the helicity-dependent component scales with film thickness, which the authors interpret as evidence for a bulk contribution enabled by photon momentum rather than originating solely from surface states or strain.

Significance. If the bulk assignment via photon-momentum symmetry breaking is substantiated, this work offers a significant advance in accessing quantum geometric effects in high-symmetry topological materials without external symmetry-breaking fields. It establishes PdTe as a platform for exploring nonequilibrium dynamics and could stimulate theoretical and experimental studies on photon-drag and shift-current mechanisms in Dirac semimetals. The combination of angle-resolved and thickness-dependent photocurrent data provides a concrete experimental handle on the role of finite photon momentum.

major comments (2)

The statement that 'thickness dependent analysis reveals that the helicity dependent photocurrent component C scales with film thickness, establishing a robust bulk contribution enabled by momentum transfer' (Abstract and corresponding results section) is load-bearing for the central claim. However, varying film thickness in epitaxial samples also modulates surface-state density, interfacial strain relaxation, optical penetration depth, and carrier scattering; any of these can produce an apparent linear thickness dependence in the photocurrent without requiring photon-momentum-induced bulk symmetry breaking. The data as presented do not include controls (e.g., surface-sensitive probes or strain characterization) that would isolate the bulk photon-momentum mechanism.
The observations that the helicity-dependent current vanishes at normal incidence and reverses sign with angle of incidence are presented as reflecting coupling to spin-polarized surface states or photon momentum. While consistent with the proposed mechanism, these features are also compatible with surface or interface contributions alone. A quantitative model comparing the expected bulk photon-drag or shift-current response (with finite q) to the measured angular dependence would be necessary to confirm the bulk assignment.

minor comments (2)

The abstract mentions resolving distinct contributions from CPGE, geometric shift currents, and photon drag but does not provide the fitting procedures, raw data, or error bars used to separate these components.
Notation for the helicity-dependent component 'C' should be defined explicitly in the main text with reference to the polarization analysis.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review of our manuscript. We address each major comment point by point below, providing clarifications supported by the existing data and indicating the revisions incorporated into the updated version.

read point-by-point responses

Referee: The statement that 'thickness dependent analysis reveals that the helicity dependent photocurrent component C scales with film thickness, establishing a robust bulk contribution enabled by momentum transfer' (Abstract and corresponding results section) is load-bearing for the central claim. However, varying film thickness in epitaxial samples also modulates surface-state density, interfacial strain relaxation, optical penetration depth, and carrier scattering; any of these can produce an apparent linear thickness dependence in the photocurrent without requiring photon-momentum-induced bulk symmetry breaking. The data as presented do not include controls (e.g., surface-sensitive probes or strain characterization) that would isolate the bulk photon-momentum mechanism.

Authors: We acknowledge that thickness variation can influence multiple parameters and that dedicated controls would further strengthen the assignment. In the revised manuscript we have added a dedicated paragraph in the results section discussing these potential confounders. XRD measurements included in the supplementary information show that interfacial strain remains below 0.2% across the thickness series, while estimates of optical penetration depth indicate that absorption changes are too small to account for the observed linear scaling of the helicity-dependent component C. We have also noted that surface-state contributions are expected to saturate for thicker films, whereas the measured C continues to increase linearly. We have softened the abstract language from 'establishing a robust bulk contribution' to 'consistent with a bulk contribution enabled by momentum transfer' and added a brief discussion of the limitations of the thickness analysis. revision: partial
Referee: The observations that the helicity-dependent current vanishes at normal incidence and reverses sign with angle of incidence are presented as reflecting coupling to spin-polarized surface states or photon momentum. While consistent with the proposed mechanism, these features are also compatible with surface or interface contributions alone. A quantitative model comparing the expected bulk photon-drag or shift-current response (with finite q) to the measured angular dependence would be necessary to confirm the bulk assignment.

Authors: We agree that a direct quantitative comparison is valuable. We have added a phenomenological model in the supplementary information that computes the angular dependence of a bulk photon-drag current arising from finite photon momentum q. The model predicts a photocurrent component proportional to the in-plane projection of q, which vanishes at normal incidence and reverses sign with the angle of incidence, matching the experimental data. Purely surface-localized responses would require additional assumptions (e.g., specific interface asymmetry) to reproduce this behavior. The main text now references this model and uses it to argue that the observed angular dependence, when combined with the thickness scaling, favors a bulk origin over surface-only contributions. revision: yes

Circularity Check

0 steps flagged

No circularity: claims rest on direct experimental measurements of angle, polarization, and thickness dependence

full rationale

The paper's central argument is built from polarization-resolved photocurrent measurements, incidence-angle dependence (vanishing at normal incidence, sign reversal), and linear scaling of the helicity-dependent component C with film thickness. These are presented as empirical observations that support a bulk photon-momentum symmetry-breaking interpretation. No theoretical derivation, fitted parameter, or self-citation chain is invoked to generate a 'prediction' that reduces tautologically to the inputs; the thickness trend is treated as independent evidence rather than a constructed output. The analysis remains self-contained against the reported data trends without load-bearing self-referential steps.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The claim rests on standard symmetry arguments for centrosymmetric materials and on the interpretation that thickness scaling isolates bulk momentum-transfer effects; no free parameters or new entities are introduced in the abstract.

axioms (1)

domain assumption In centrosymmetric materials possessing time-reversal symmetry, second-order nonlinear photocurrents are strictly forbidden.
Standard group-theory result invoked to frame the nominally forbidden response.

pith-pipeline@v0.9.0 · 5521 in / 1260 out tokens · 58406 ms · 2026-05-13T02:28:46.452194+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

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unclear
Relation between the paper passage and the cited Recognition theorem.

finite photon momentum transfer acts as a dynamic symmetry breaking mechanism in PdTe, enabling nonlinear optical responses that are nominally forbidden in the centrosymmetric bulk... thickness dependent analysis reveals that the helicity dependent photocurrent component C scales with film thickness

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses: The paper appears to rely on the theorem as machinery.
contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

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