Optical detection of the sliding ferroelectric switching in hBN with a WSe2 monolayer

Benjamin Lassagne; Cedric Robert; Jules Frauni\'e; Kenji Watanabe; S\'ebastien Roux; Takashi Taniguchi

Optical detection of the sliding ferroelectric switching in hBN with a WSe2 monolayer

T0 review · 0 major / 5 minor · reviewed 2026-08-11 · deepseek-v4-flash

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Pith's one-line read The photoluminescence ratio of trions to excitons in a WSe2 monolayer is demonstrated to be an optical readout of ferroelectric switching in an adjacent hBN interface.

desk verdict First optical readout of sliding ferroelectric switching in hBN, with a solid multi-technique evidence package; send to review. read the letter →

arxiv 2412.12703 v1 pith:62TX6DJV submitted 2024-12-17 cond-mat.mtrl-sci cond-mat.mes-hall

Sébastien Roux , Jules Fraunié , Kenji Watanabe , Takashi Taniguchi , Benjamin Lassagne , Cedric Robert This is my paper · ORCID

classification cond-mat.mtrl-scicond-mat.mes-hall

keywords slidingferroelectricityhexagonalboronnitridevanderWaalsheterostructureWSe2monolayerphotoluminescencetrionferroelectricswitchingnon-volatilememory

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper reports that a single layer of WSe2 placed a few nanometres from a ferroelectric interface in hexagonal boron nitride can act as an optical readout of that interface's polarization state. In a stack of two parallel hBN layers, AB and BA stacking produce opposite out-of-plane electric polarizations, and an applied field can switch between them by sliding the layers. The authors show that the photoluminescence ratio of negative trions to neutral excitons in the WSe2 monolayer follows the local polarization, so optical maps reveal the ferroelectric domains and their switching. This matters because it offers a non-destructive, local, contact-free probe of sliding ferroelectricity, potentially useful for compact non-volatile memory and for studying switching dynamics.

What carries the argument

The central object is the photoluminescence ratio of the negatively charged trion (the singlet negative trion $X_S^-$) to the neutral exciton $X_0$ in the WSe2 monolayer; this ratio grows with electron doping. The mechanism that carries the argument is sliding ferroelectricity at the hBN-hBN interface: AB and BA stacking produce opposite out-of-plane polarizations, and an in-plane sliding of one layer by one bond length switches between them. The ferroelectric polarization imprints a local electron-doping modulation on the adjacent WSe2 via capacitive coupling, shifting the gate potential by roughly $\pm100$ mV for the two domain types. The PL ratio is measured at 4 K under 1.96 eV excitation with a confocal microscope, giving a spatial resolution of about 500 nm.

What would settle it

Measure the same gate-voltage-dependent $X_S^-/X_0$ shift and hysteresis in a double-gated device where the WSe2 monolayer is held at a fixed carrier density while the hBN interface is poled; if the 200 mV shift and the square hysteresis disappear when the doping is fixed, the capacitive-coupling interpretation is wrong. Alternatively, a control stack with an identically prepared hBN interface but no ferroelectric domains should show no shift or hysteresis.

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Extended reading notes

Core claim

The central claim is that the photoluminescence of a remote WSe2 monolayer can be used to detect polarization switching in a sliding ferroelectric hBN interface. Experimentally, after applying an out-of-plane electric field of $+0.11$ V/nm, the gate-voltage dependence of the trion-to-exciton PL ratio is shifted by about 200 mV compared with after applying $-0.11$ V/nm; the shift is attributed to the FE polarization changing the capacitive coupling between the WSe2 and the graphite back gate, modulating the electron density by roughly $3\times10^{10}$ cm$^{-2}$. Under zero bias, maps of the $X_S^-/X_0$ ratio show two domain populations whose areas change after opposite poling, and the ratio at a fixed point traces reproducible square hysteresis cycles with switching fields of $+0.065\pm0.001$ V/nm and $-0.098\pm0.002$ V/nm, with a 16.5 mV/nm imprint. The paper concludes that the WSe2 monolayer is a local optical probe of the AB/BA ferroelectric state.

Load-bearing premise

The photoluminescence ratio $X_S^-/X_0$ is an undistorted local measure of electron doping in the WSe2 monolayer, and the doping difference between AB and BA domains comes from the hBN ferroelectric polarization rather than from trapped charges, laser-induced effects, or transfer strain.

Editorial extensions

If this is right

A non-destructive, local optical readout of ferroelectric domains in hBN is available without contacting the WSe2 layer.
Ferroelectric switching in hBN can be mapped with diffraction-limited resolution, revealing partial switching and pinning at small domains.
The reproducible square hysteresis of the PL ratio offers a route to optically reading non-volatile polarization states in memory devices.
Because the probe is the PL ratio, it must be operated near the WSe2 neutrality point where the FE-induced doping dominates over gate doping.
Double-gated devices should allow independent control of electric field and doping, enabling studies of switching dynamics and domain-wall speed.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

This suggests the same trion-to-exciton PL readout should work with other monolayer transition metal dichalcogenides, since the coupling is generic to any semiconductor monolayer in capacitive contact with a ferroelectric hBN interface.
Time-resolved or stroboscopic PL measurements could extend this static readout to track domain-wall motion during switching.
The observed 16.5 mV/nm imprint implies an internal field not explained by electrode work-function asymmetry; identifying its microscopic origin could lead to engineered pinning or deterministic switching.
The 200 mV gate-voltage shift is itself a non-volatile electrical signature; combined with optical readout it suggests a memory cell where writing is electrical and reading is all-optical.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Quick take: this is the first optical detection of switching in sliding ferroelectric hBN, and the evidence is solid. The paper deserves a serious referee.

The new thing is straightforward: the authors use a remote WSe2 monolayer as a local photoluminescence readout of the AB/BA domain state in a ferroelectric hBN interface, and they actively switch the domains with an out-of-plane field. That wasn't in their earlier static work or anyone else's. The demonstration combines KFM domain imaging, PL maps that reverse after opposite poling, sharp and reproducible hysteresis loops measured at zero readout bias, and a control device without the FE interface. That is a convincing package. The hysteresis loops are square, repeat four times, and the transition fields are consistent with known coercive fields for sliding hBN. They also honestly report that switching is incomplete and that there is an imprint of about 16 mV/nm they cannot fully explain. No free parameters are fit to produce the central result.

Soft spots, in proportion: the single-gate geometry couples the poling field to electrostatic doping in the WSe2, so the 200 mV shift in the gate-voltage axis after opposite poling is interpreted as a change in capacitive coupling rather than directly measured. The measurement at zero bias and the control sample largely separate the remanent polarization from the instantaneous field effect, but trapped charge at the interface mimicking polarization is not fully excluded. That is a minor caveat, not a load-bearing flaw. The imprint discussion is honest but open-ended.

The paper is well-written, the SI provides useful supporting data, and the claims match the evidence. It is an incremental but real advance for the sliding ferroelectric community. I would send it to peer review: a good referee can probe the control sample details and the capacitive model, but the core observation looks solid.

Referee Report

0 major / 5 minor

Summary. The manuscript reports the optical detection of ferroelectric switching in a sliding hBN interface via the photoluminescence (PL) of an adjacent WSe2 monolayer. The authors fabricate a graphite-FE hBN-WSe2 stack, identify AB and BA ferroelectric domains by Kelvin force microscopy (KFM), and show that the PL intensity ratio of the negative trion to the neutral exciton (Xs-/X0) maps the same domains. After applying out-of-plane electric fields above the expected switching threshold, they observe a ~200 mV shift in the gate-voltage dependence of the trion onset, PL maps in which the BA/AB domain areas reverse with poling, and reproducible square hysteresis loops measured at zero bias, with a horizontal imprint of 16.5 mV/nm. A control device without the FE interface shows no such hysteresis. The authors interpret these observations as demonstrating that a remote WSe2 monolayer can serve as a local, non-destructive optical probe of sliding ferroelectric switching in hBN.

Significance. If correct, this result provides a new optical readout modality for sliding ferroelectric hBN, with diffraction-limited spatial resolution and simpler device fabrication than electrical or electron-microscopy probes. The claim is supported by several independent pieces of evidence: KFM-to-PL correlation, the appearance of the gate-voltage shift only after fields above the switching threshold, the absence of hysteresis in a control sample without the FE interface, and the sharpness of the switching transitions at fields consistent with literature values. The approach builds on the authors' prior work (ref 35) linking FE domains to doping, and no free parameter is fitted to produce the central observations. The main limitations—single-gate geometry coupling field and doping, incomplete domain switching, and the lack of a full microscopic explanation of the imprint—are explicitly acknowledged and do not undermine the central demonstration.

minor comments (5)

[Fig. 2 and Fig. 3] The interpretation that the optical changes reflect ferroelectric switching would be further strengthened by post-switching KFM images on the same area; the initial KFM image in Fig. 1(c) is taken before any poling, so a direct confirmation that the PL-detected BA/AB assignment after poling matches the stacking would remove residual ambiguity about trapped-charge effects. The authors should at least state this limitation explicitly where the switching maps are presented.
[Fig. 2(c) and Fig. 1(d)] The 200 mV gate-voltage shift is stated to be comparable to the KFM surface potential contrast, but the line scan in Fig. 1(d) shows only about 115 mV. The authors should clarify whether the relevant potential at the WSe2 position is expected to be larger than the top-surface KFM contrast, or adjust the comparison accordingly.
[Throughout] The notation for the negatively charged trion is inconsistent (XS-, Xs-, X S-); a single symbol should be used consistently throughout the text and figures.
[Fig. 1(e) caption] The caption states the PL spectra were measured under 10 µW excitation, while all other measurements in the paper use 1 µW; please specify whether the ratio Xs-/X0 is power-dependent in the relevant regime, or justify the different excitation power.
[Fig. 3(c)] The four hysteresis cycles show a slight decrease in the high-ratio level after successive cycles; a brief comment on the reproducibility and possible fatigue or drift would be useful.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the WSe2 PL readout of hBN ferroelectric switching is a direct experimental observation, not a fitted or self-referential derivation.

full rationale

The paper's central claim—that a remote WSe2 monolayer can optically read the polarization state of a sliding ferroelectric hBN interface—is not derived from an input that already contains the conclusion. The readout quantity Xs-/X0 is not fitted to the FE state; it is a direct photoluminescence measurement, and its assignment to AB versus BA domains is anchored by KFM surface-potential images on the same structure (Fig. 1(c-f)). The switching claim rests on direct observations: the ~200 mV shift in the gate-voltage dependence of the trion onset appears only after applying fields above the expected switching threshold and is absent in a control device without FE domains (SI Fig. S4); PL maps after +0.14 and -0.14 V/nm show reversal of domain areas (Fig. 3(a-b)); and the PL ratio measured at 0 V traces reproducible square hysteresis loops with sharp transitions (Fig. 3(c-d)). No parameter is fitted to the target result, and no equation is used in both premise and conclusion. The paper does rely on the authors' prior observation (ref. 35) that FE hBN domains dope an adjacent WSe2 monolayer, and on the general identification of negative-trion PL with electron doping; these are normal uses of prior empirical results rather than circular inputs, and the present data—KFM correlation plus the FE-free control—provide independent support within the paper itself. The acknowledged limitations, such as the single-gate geometry coupling the poling field to electrostatic doping and possible trapped-charge mimics of polarization, are correctness risks or alternative explanations, not evidence that the derivation is equivalent to its inputs. No circular step can be quoted from the paper.

Assumptions & free parameters 0 free parameters · 4 assumptions · 0 invented entities

The central claim rests on the established domain-to-doping correspondence, the single-switchable-interface assumption, and the control experiment. No new particles or forces are introduced, and no empirical constant is fitted to make the result work.

assumptions (4)

domain assumption The WSe2 PL ratio Xs-/X0 is a monotonic local reporter of electron doping, and FE domains of hBN modulate that doping.
Used throughout Figs. 2 and 3 to convert PL maps and hysteresis into polarization states; grounded in the authors' earlier work (ref 35) and KFM data.
domain assumption The AB/BA stacking at the torn hBN interface is the only source of switchable out-of-plane polarization in the stack, and switching proceeds by layer sliding.
The sample's ferroelectric character is established by KFM before transfer and by comparison with known hBN sliding ferroelectricity (refs 14-16).
domain assumption Bias-induced charge trapping and drift do not produce the observed 200 mV shift; the non-FE control sample isolates the FE contribution.
The attribution of the vertical shift to FE switching rests on this, supported by SI Fig. S4.
standard math The parallel-plate capacitor model Delta n = epsilon0 epsilon_hBN / (e t) Delta V describes the gate-induced carrier density change.
Used in the SI to convert bias to carrier density and electric field, with hBN thickness 122 nm and permittivity 3.4.

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Cite this review

Pith. "Pith review of Optical detection of the sliding ferroelectric switching in hBN with a WSe2 monolayer." pith.science (2026). https://pith.science/paper/62TX6DJV

@misc{pith2026241212703,
  author       = {Pith},
  title        = {Pith review of: Optical detection of the sliding ferroelectric switching in hBN with a WSe2 monolayer},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/62TX6DJV}},
  note         = {Machine review of arXiv:2412.12703}
}

read the original abstract

When two BN layers are stacked in parallel in an AB or BA arrangement, a spontaneous out-of-plane electric polarization arises due to charge transfer in the out-of-plane B-N bonds. The ferroelectric switching from AB to BA (or BA to AB) can be achieved with a relatively small out-of-plane electric field through the in-plane sliding of one atomic layer over the other. However, the optical detection of such ferroelectric switching in hBN has not yet been demonstrated. In this study, we utilize an adjacent WSe2 monolayer to detect the ferroelectric switching in BN. This dynamic coupling between a 2D ferroelectric and a 2D semiconductor allows for the fundamental investigation of the ferroelectric material using a non-destructive, local optical probe, offering promising applications for compact and non-volatile memory devices.

Figures

Figures reproduced from arXiv: 2412.12703 by the authors.

**Figure 1.** (e) shows typical PL spectra of the WSe2 ML emission taken at 4 K and measured above the AB domain, in dark blue, and above the BA domain, in light blue. The reference energy is fixed at the position of the neutral exciton X0 . As shown in ref. 35, the ferroelectric domains induce a modulation of the doping on the WSe2 monolayer. Here, the doping modulation is smaller than that in Ref. 35 which was conducted at 55 K… view at source ↗

**Figure 3.** (a) shows a mapping of the Xs- / X0 PL ratio measured at 0V after application of a +0.14 V.nm-1 electric field (pointing upwards). In the region highlighted by the yellow solid lines we observe an alternance of two white domains (BA stacking in hBN with upwards polarization) and two dark blue domains (AB stacking in hBN with downwards polarization) [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

9 extracted references · 5 canonical work pages

[1]

Nevertheless, their use in practical devices requires epitaxial growth of thin films

For the past decades, most of the studies have focused on FE materials with three -dimensional (3D) crystal structures. Nevertheless, their use in practical devices requires epitaxial growth of thin films. Unfortunately, the reduction of thickness generally goes along with an increase of the depolarizing field. Moreover, the integration of these tradition...

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Programme des Investissements d’Avenir

Future perspectives include the fabrication of double gated devices to control independently the out-of-plane electric field and the electrostatic doping in the WSe2 ML. Such device could be used to optically study switching dynamics and measure domain walls speed as electric field could be applied while keeping the WSe 2 ML close to neutrality. Reducing ...

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Together with the high numerical aperture of the objective (NA=0.82), it guarantees a spatial resolution of about 500 nm

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Shortly after, similar observations were made with parallelly aligned transition metal dichalcogenide (TMD) bilayers 17,18 and even with graphene

The experimental demonstrations came in 2021, when FE was observed in marginally twisted layers of hexagonal boron nitride (hBN) 14–16. Shortly after, similar observations were made with parallelly aligned transition metal dichalcogenide (TMD) bilayers 17,18 and even with graphene

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https://doi.org/10.1038/s41467-021-25747-5. (4) Taniguchi, T.; Watanabe, K. Synthesis of High-Purity Boron Nitride Single Crystals under High Pressure by Using Ba–BN Solvent. Journal of Crystal Growth 2007, 303 (2), 525–529. https://doi.org/10.1016/j.jcrysgro.2006.12.061. (5) Fraunié, J.; Jamil, R.; Kantelberg, R.; Roux, S.; Petit, L.; Lepleux, E.; Pachec...

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https://doi.org/10.1021/acsnano.7b02756. (14) Yasuda, K.; Wang, X.; Watanabe, K.; Taniguchi, T.; Jarillo-Herrero, P. Stacking-Engineered Ferroelectricity in Bilayer Boron Nitride. Science 2021, 372 (6549), 1458–1462. https://doi.org/10.1126/science.abd3230. (15) Woods, C. R.; ...

2021 doi

Pith tools

Reviewed August 11, 2026 · model on record in the stance chip above.

[1] [1]

Nevertheless, their use in practical devices requires epitaxial growth of thin films

For the past decades, most of the studies have focused on FE materials with three -dimensional (3D) crystal structures. Nevertheless, their use in practical devices requires epitaxial growth of thin films. Unfortunately, the reduction of thickness generally goes along with an increase of the depolarizing field. Moreover, the integration of these tradition...

work page 2017

[2] [2]

Programme des Investissements d’Avenir

Future perspectives include the fabrication of double gated devices to control independently the out-of-plane electric field and the electrostatic doping in the WSe2 ML. Such device could be used to optically study switching dynamics and measure domain walls speed as electric field could be applied while keeping the WSe 2 ML close to neutrality. Reducing ...

work page 2023

[3] [5]

Together with the high numerical aperture of the objective (NA=0.82), it guarantees a spatial resolution of about 500 nm

For the mapping, the sample is moved with respect to the laser spot using a xyz piezodriven scanner from Attocube. Together with the high numerical aperture of the objective (NA=0.82), it guarantees a spatial resolution of about 500 nm. Carrier density as a function of the gate voltage The carrier density is estimated from the simple plate capacitance mod...

2014

[4] [13]

Shortly after, similar observations were made with parallelly aligned transition metal dichalcogenide (TMD) bilayers 17,18 and even with graphene

The experimental demonstrations came in 2021, when FE was observed in marginally twisted layers of hexagonal boron nitride (hBN) 14–16. Shortly after, similar observations were made with parallelly aligned transition metal dichalcogenide (TMD) bilayers 17,18 and even with graphene

work page 2021

[5] [347]

(16) Vizner Stern, M.; Waschitz, Y.; Cao, W.; Nevo, I.; Watanabe, K.; Taniguchi, T.; Sela, E.; Urbakh, M.; Hod, O.; Ben Shalom, M

https://doi.org/10.1038/s41467-020-20667-2. (16) Vizner Stern, M.; Waschitz, Y.; Cao, W.; Nevo, I.; Watanabe, K.; Taniguchi, T.; Sela, E.; Urbakh, M.; Hod, O.; Ben Shalom, M. Interfacial Ferroelectricity by van Der Waals Sliding. Science 2021, 372 (6549), 1462–1466. https://doi.org/10.1126/science.abe8177. (17) Wang, X.; Yasuda, K.; Zhang, Y.; Liu, S.; Wa...

work page doi:10.1038/s41467-020-20667-2

[6] [1389]

(27) Liang, J.; Yang, D.; Wu, J.; Dadap, J

https://doi.org/10.1038/s41467-024-45709-x. (27) Liang, J.; Yang, D.; Wu, J.; Dadap, J. I.; Watanabe, K.; Taniguchi, T.; Ye, Z. Optically Probing the Asymmetric Interlayer Coupling in Rhombohedral-Stacked ${\mathrm{MoS}}_{2}$ Bilayer. Phys. Rev. X 2022, 12 (4), 041005. https://doi.org/10.1103/PhysRevX.12.041005. (28) Dean, C. R.; Young, A. F.; Meric, I.; ...

arXiv

[7] [2024]

(24) Kim, I.-J.; Lee, J.-S

https://doi.org/10.48550/arXiv.2407.15081. (24) Kim, I.-J.; Lee, J.-S. Ferroelectric Transistors for Memory and Neuromorphic Device Applications. Advanced Materials 2023, 35 (22), 2206864. https://doi.org/10.1002/adma.202206864. (25) Leblanc, C.; Song, S.; Jariwala, D. 2D Ferroelectrics and Ferroelectrics with 2D: Materials and Device Prospects. Current O...

arXiv doi:10.48550/arxiv.2407.15081 2023

[8] [5455]

(4) Taniguchi, T.; Watanabe, K

https://doi.org/10.1038/s41467-021-25747-5. (4) Taniguchi, T.; Watanabe, K. Synthesis of High-Purity Boron Nitride Single Crystals under High Pressure by Using Ba–BN Solvent. Journal of Crystal Growth 2007, 303 (2), 525–529. https://doi.org/10.1016/j.jcrysgro.2006.12.061. (5) Fraunié, J.; Jamil, R.; Kantelberg, R.; Roux, S.; Petit, L.; Lepleux, E.; Pachec...

work page doi:10.1038/s41467-021-25747-5 2007