Pith. sign in

REVIEW 3 major objections 4 minor 33 references

Observation of 1/3 fractional quantum Hall physics in balanced large angle twisted bilayer graphene

T0 review · 3 major / 4 minor · reviewed 2026-08-11 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗ Review JSON

Pith's one-line read The paper reports that in balanced large-angle twisted bilayer graphene, the ground state at total filling 1/3 is an interlayer coherent excitonic superfluid of fractional charges, with the same topological order as the 1/3 Laughlin state…

desk verdict Solid experimental observation of a quantized 1/3 FQH plateau in balanced large-angle twisted bilayer graphene; the (333) identification needs the SI before it can be evaluated, but that gap does not undermine the core experimental result. read the letter →

arxiv 2412.09210 v1 pith:VFULCJYG submitted 2024-12-12 cond-mat.mes-hall cond-mat.str-el

Dohun Kim , Seyoung Jin , Takashi Taniguchi , Kenji Watanabe , Jurgen H. Smet , Gil Young Cho , Youngwook Kim This is my paper · ORCID
classification cond-mat.mes-hallcond-mat.str-el
keywords fractionalquantumHalleffecttwistedbilayergrapheneinterlayerexcitoncondensate(333)stateLaughlinMonteCarlosimulationdisplacementfieldquantizedplateau
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

Large-angle twisted bilayer graphene brings two electron layers within $0.33$ nm while the twist suppresses single-particle tunneling, so interlayer Coulomb interactions are far stronger than in semiconductor bilayers. The paper reports a fractional quantum Hall state at total filling $\nu_{\text{tot}}=1/3$ for balanced layer population, and Monte Carlo energetics identify it as the $(333)$ state: an excitonic superfluid whose excitons are made of quasiparticles of charge $+1/3$ and $-1/3$. This state has the same topological order as a single-layer $1/3$ Laughlin state, but its wave function is spread coherently across both layers. The same simulations account for displacement-field-driven transitions to layer-polarized states at $1/3$, $2/3$, $4/3$, $8/5$, and $5/3$ filling.

What carries the argument

The central object is the $(333)$ trial wave function, a two-component state in which same-layer and opposite-layer electron pairs both get the same Jastrow factor, $(z_i-z_j)^3$, giving total filling $1/3$ with equal occupation of both layers. It is the workhorse of the argument because Monte Carlo energy evaluation selects it as the ground state at zero displacement field and shows it loses to a layer-polarized $1/3$ Laughlin state as the displacement field grows. The energy calculations use a Hamiltonian for large-angle twisted bilayer graphene that combines Coulomb interaction, displacement-field potential, capacitive energy, and a phenomenological short-range term, with candidate states including composite-fermion, pseudospin-singlet, and interlayer-coherent wave functions. The physical mechanism that makes the state possible is the atomic layer spacing of $0.33$ nm: with magnetic length $l_B$, the interlayer-to-intralayer Coulomb ratio $l_B/d$ can reach about $20$, far beyond what semiconductor bilayers achieve.

What would settle it

A decisive check is to measure the Hall conductivity at $\nu_{\text{tot}}=-1/3$ and zero displacement field in a device free of contact saturation; the claimed state requires a true plateau at $\sigma_{xy}=-(1/3)e^2/h$ that persists over a range of magnetic field and temperature. A second check is to rerun the Monte Carlo comparison with varied strengths of the short-range interaction and with trial states outside the selected set, such as two decoupled $1/3$ Laughlin layers; if any of these beats the $(333)$ state, the identification fails.

Watch

Extended reading notes

Core claim

The central claim is that, for balanced population and zero displacement field, the ground state at $\nu_{\text{tot}}=1/3$ is the interlayer coherent two-component $(333)$ state, the fractional analogue of the $(111)$ state seen at integer filling. Excitons form out of quasiparticles with fractional charge $+1/3$ and $-1/3$; their Bose-Einstein condensation makes the state incompressible. Topologically the $(333)$ state is identical to the $1/3$ Laughlin state, with the same ground-state degeneracy on a torus and the same fractional excitations, but the wave function is shared equally and coherently by the two layers. When the displacement field is increased, the $(333)$ state gives way to a fully layer-polarized single-component $1/3$ Laughlin state. The paper supports this assignment with a quantized Hall plateau at $\nu_{\text{tot}}=-1/3$ in one device, minima at $1/3$ in four devices, and Monte Carlo energy comparisons over a set of candidate trial states.

Load-bearing premise

The theoretical assignment of the $1/3$ state rests on Monte Carlo energies computed with a Hamiltonian that includes a phenomenological short-range interaction term whose strength is not stated in the main text; the identification is only as secure as that model choice.

Editorial extensions

If this is right

  • If the assignment is right, large-angle twisted bilayer graphene is a platform for fractional exciton condensates, extending the integer $(111)$ exciton superfluid to a state built from fractional charges.
  • The displacement field becomes a tuning knob that switches between an interlayer-coherent fractional state and a layer-polarized $1/3$ Laughlin state without changing the topological order.
  • The measured quantized transport at $\nu_{\text{tot}}=-1/3$ should carry Hall conductance exactly $-(1/3)e^2/h$ in the interlayer-coherent regime.
  • The same Monte Carlo procedure predicts the ground states and transition fillings at $2/3$, $4/3$, $8/5$, and $5/3$, giving a testable phase diagram for future devices.

Reading between the lines

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

  • Not reported here: interlayer counterflow or tunnelling spectroscopy. An excitonic superfluid should show a sharp interlayer transport anomaly even though single-particle tunnelling is suppressed by the twist-induced momentum mismatch.
  • Shot-noise or local charge sensing could test the fractional charge $e/3$ of the quasiparticles inside the coherent state, distinguishing a true fractional exciton condensate from two independent Laughlin layers.
  • If the short-range interaction parameter is fixed independently, the Monte Carlo phase diagram becomes a quantitative prediction; measuring the critical displacement field at which the $1/3$ state loses coherence would test it directly.
  • The same physics may appear at other fillings where trial states with interlayer coherence are energetically competitive, suggesting a broader family of fractional excitonic states in this platform.
Share X Bluesky LinkedIn Reddit HN

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

3 major / 4 minor

Summary. The manuscript reports magnetotransport measurements on four large-angle twisted bilayer graphene devices and observes a conductivity minimum at total filling νtot = 1/3 under balanced layer population, together with a quantized Hall plateau at σxy = -1/3 e²/h in device D2. The authors interpret this state as an interlayer-coherent two-component (333) state, the fractional analogue of the (111) excitonic superfluid, based on Monte Carlo energy comparisons among trial wave functions. They also report displacement-field-driven transitions at several fractional fillings and compare the observed features with a calculated phase diagram.

Significance. If correct, the result would demonstrate an excitonic superfluid made of fractional charges, with the same topological properties as the single-layer 1/3 Laughlin state but with the wave function spread coherently across both layers. The experimental evidence is a clear strength: the 1/3 feature appears in multiple devices, develops with magnetic field, and a Hall plateau is observed at -1/3. The theoretical comparison covers several fillings and explicitly identifies states with different symmetry and topology. The main weakness is that the central identification rests on Monte Carlo simulations whose Hamiltonian includes a phenomenological short-range interaction term whose value, and the energy differences with statistical errors, are not reported in the posted manuscript. This gap is load-bearing because the unique claim of the paper is not just the existence of a 1/3 incompressible state, but its assignment to the interlayer-coherent (333) state.

major comments (3)
  1. [Methods, Monte Carlo simulation] The Hamiltonian used for the phase diagram contains a phenomenological short-range interaction term, but neither its strength nor the full model parameters (dielectric constant, screening, capacitive energy) are stated in the main text; the details are deferred to Supplementary Notes 4–7. Since the identification of the νtot = 1/3 ground state as the (333) state, and the phase boundaries in Fig. 2(a), are decided by energy differences among trial wave functions, this missing parameter makes the central theoretical claim unreproducible from the posted manuscript. Please report the interaction strength, the Hamiltonian, and the Monte Carlo energy differences with statistical error bars for the competing states at νtot = 1/3.
  2. [Theoretical phase diagram, Fig. 2(a)] The Monte Carlo comparison is performed only over a finite set of trial wave functions; the paper does not state that the true ground state is guaranteed to be in this set or provide any unbiased check, such as exact diagonalization of small systems with the same Hamiltonian. The assertion that the balanced 1/3 state is the interlayer-coherent (333) state is therefore conditional on this assumption. Please state this assumption explicitly or add a small-system exact-diagonalization confirmation.
  3. [Results, Magnetotransport data; Fig. 1(a)] The text states that the simulated phase diagram in Fig. 2(a) shows 'reasonable agreement' with the transport data, but no quantitative criterion is given for matching conductivity minima and transition features to the calculated state changes. Because the simulations are the sole basis for identifying the nature of the states, at least one quantitative comparison (for example, the displacement field of a transition at a fixed filling, or an estimated energy gap at B = 19 T) would substantially strengthen the claim.
minor comments (4)
  1. [Fig. 1 caption, panel (e)] The label 'Dv/εint' in panel (e) appears to be a typo for 'D/εint'; please correct it.
  2. [Methods, Monte Carlo simulation] The sentence 'The algorithm is ahead optimized by acceptance rates and integrated autocorrelation times computed from the pre-run data' is unclear; please rephrase, for example as 'The algorithm is optimized using acceptance rates and integrated autocorrelation times computed from pre-run data.'
  3. [Fig. 3(b)] The text should state explicitly that the lock-in saturation artefact is confined to the region near charge neutrality and does not affect the plateau at νtot = -1/3, since the plateau is a central quantitative result.
  4. [General presentation] The main text repeatedly refers to Supplementary Notes 4–10 for the Hamiltonian, trial wave functions, and topological properties; the arXiv version lacks these notes, so the preprint is not self-contained. Please ensure the Supplementary Information is included with the submission or summarize the essential equations in the main text.

Circularity Check

0 steps flagged · score 2.0 of 10

The 1/3 FQH observation is self-contained, but the assignment to the interlayer-coherent (333) state is model-dependent: the Monte Carlo Hamiltonian inherits an unquantified 'phenomenological short-range interaction term' from the authors' prior work, so the theoretical identification is a verifiability gap rather than a construction-level circularity.

full rationale

The experimental result, a locked 1/3 Hall plateau at balanced filling, is an independent measurement. The theoretical step is an explicit Monte Carlo energy comparison among named trial wave functions, so the (333) assignment is not analytically identical to the input Hamiltonian. However, the Hamiltonian includes a 'phenomenological short-range interaction term' (Methods) whose value is not given in the posted text and whose origin is attributed to refs [12,23], with [12] being the authors' own previous paper. The energy differences and the construction of the trial states are deferred to SI Notes 4-7, which are not part of this arXiv version; consequently the central theoretical claim is conditional on an unstated parameter and cannot be independently reproduced from the posted manuscript. That is a genuine load-bearing gap in verifiability, but the text does not state that the term was fitted to the observed fractional states or make the (333) conclusion equivalent to an input by an equation. Figure 2 is drawn only at fillings already observed to have minima, so the simulations are interpretive and postdictive rather than a free-standing prediction; this further lowers their confirmatory force without making the argument circular. Under the rubric this warrants a low score: one self-citation contributes to the model, while the experimental and variational content remain independent.

Assumptions & free parameters 1 free parameters · 3 assumptions · 0 invented entities

The central interpretation as a (333) interlayer coherent state relies on a model Hamiltonian with a phenomenological short-range interaction term whose value is not given in the main text. The trial wave function set is selected by the authors and may not be exhaustive. The suppression of interlayer tunneling is an assumed property of large-angle twisted bilayer graphene.

free parameters (1)
  • Phenomenological short-range interaction strength = not disclosed in main text
    Appears in the Hamiltonian in the Monte Carlo simulation section; its value can affect the energy ordering of the candidate trial states and is not stated in the main text.
assumptions (3)
  • domain assumption Interlayer tunneling is effectively suppressed by the large twist angle momentum mismatch.
    Invoked in the Introduction (and references 10-14) to justify treating the two layers as weakly coupled but strongly interacting via Coulomb forces.
  • domain assumption The Hamiltonian consists of Coulomb, displacement field, capacitive, and short-range interaction terms.
    The Monte Carlo simulation uses this model (Methods, MC simulation). The short-range term is phenomenological and its origin is not derived from first principles.
  • ad hoc to paper The selected trial wave functions include the actual ground state for each filling and displacement field.
    The energy minimization is over a finite set of candidate states (e.g., Halperin (333), pseudospin singlet, Laughlin, composite fermion states). If the true ground state is outside this set, the conclusions could change.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Observation of 1/3 fractional quantum Hall physics in balanced large angle twisted bilayer graphene." pith.science (2026). https://pith.science/paper/VFULCJYG

@misc{pith2026241209210,
  author       = {Pith},
  title        = {Pith review of: Observation of 1/3 fractional quantum Hall physics in balanced large angle twisted bilayer graphene},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/VFULCJYG}},
  note         = {Machine review of arXiv:2412.09210}
}
read the original abstract

Magnetotransport of conventional semiconductor based double layer systems with barrier suppressed interlayer tunneling has been a rewarding subject due to the emergence of an interlayer coherent state that behaves as an excitonic superfluid. Large angle twisted bilayer graphene offers unprecedented strong interlayer Coulomb interaction, since both layer thickness and layer spacing are of atomic scale and a barrier is no more needed as the twist induced momentum mismatch suppresses tunneling. The extra valley degree of freedom also adds richness. Here we report the observation of fractional quantum Hall physics at 1/3 total filling for balanced layer population in this system. Monte Carlo simulations support that the ground state is also an excitonic superfluid but the excitons are composed of fractional rather than elementary charges. The observed phase transitions with an applied displacement field at this and other fractional fillings are also addressed with simulations. They reveal ground states with different topology and symmetry properties.

Figures

Figures reproduced from arXiv: 2412.09210 by the authors.

Figure 1
Figure 1. FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p007_1.png] view at source ↗
Figure 2
Figure 2. FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p008_2.png] view at source ↗
Figure 3
Figure 3. FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗
Figures from the paper (1 more)
Figure 4
Figure 4. Figure 4: FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p010_4.png]

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

33 extracted references · 26 canonical work pages

  1. [1]

    R. D. Wiersma, J. G. S. Lok, S. Kraus, W. Dietsche, K. von Klitzing, D. Schuh, M. Bichler, H.-P. Tranitz, and W. Wegscheider, Activated transport in the separate lay- ers that form theνT = 1exciton condensate, Phys. Rev. Lett. 93, 266805 (2004)

    work page 2004

  2. [2]

    Kellogg, J

    M. Kellogg, J. P. Eisenstein, L. N. Pfeiffer, and K. W. West, Vanishing Hall resistance at high magnetic field in a double-layer two-dimensional electron system, Phys. Rev. Lett. 93, 036801 (2004)

    work page 2004

  3. [3]

    Tutuc, M

    E. Tutuc, M. Shayegan, and D. A. Huse, Counterflow 5 measurements in strongly correlated GaAs hole bilayers: evidence for electron-hole pairing, Phys. Rev. Lett. 93, 036802 (2004)

    work page 2004

  4. [4]

    Zhang, W

    D. Zhang, W. Dietsche, and K. von Klitzing, Anoma- lous interlayer transport of quantum Hall bilayers in the strongly Josephson-coupled regime, Phys. Rev. Lett.116, 186801 (2016)

    work page 2016

  5. [5]

    Zhang, J

    D. Zhang, J. Falson, S. Schmult, W. Dietsche, and J. H. Smet, Quasiparticle tunneling across an exciton conden- sate, Phys. Rev. Lett.124, 246801 (2020)

    work page 2020

  6. [6]

    X. Liu, K. Watanabe, T. Taniguchi, B. I. Halperin, and P. Kim, Quantum Hall drag of exciton condensate in graphene, Nat. Phys.13, 746–750 (2017)

    work page 2017

  7. [7]

    J. I. A. Li, T. Taniguchi, K. Watanabe, J. Hone, and C. R. Dean, Excitonic superfluid phase in double bilayer graphene, Nat. Phys.13, 751–755 (2017)

    work page 2017

  8. [8]

    X. Liu, Z. Hao, K. Watanabe, T. Taniguchi, B. I. Halperin, and P. Kim, Interlayer fractional quantum Hall effect in a coupled graphene double layer, Nat. Phys.15, 893–897 (2019)

    work page 2019

Show all 33 references
  1. [9]

    J. I. A. Li, Q. Shi, Y. Zeng, K. Watanabe, T. Taniguchi, J. Hone, and C. R. Dean, Pairing states of composite fermionsindouble-layergraphene,Nat.Phys. 15,898–903 (2019)

    2019

  2. [10]

    Y. Kim, H. Yun, S.-G. Nam, M. Son, D. S. Lee, D. C. Kim, S. Seo, H. C. Choi, H.-J. Lee, S. W. Lee, and J. S. Kim, Breakdown of the interlayer coherence in twisted bilayer graphene, Phys. Rev. Lett.110, 096602 (2013)

    2013

  3. [11]

    Y. Kim, P. Moon, K. Watanabe, T. Taniguchi, and J. H. Smet, Odd integer quantum Hall states with interlayer coherence in twisted bilayer graphene, Nano Lett. 21, 4249–4254 (2021)

    2021

  4. [12]

    D.Kim, B.Kang, Y.-B.Choi, K.Watanabe, T.Taniguchi, G.-H. Lee, G. Y. Cho, and Y. Kim, Robust interlayer- coherent quantum Hall states in twisted bilayer graphene, Nano Lett. 23, 163 (2023)

    2023

  5. [13]

    S. Kim, D. Kim, K. Watanabe, T. Taniguchi, J. H. Smet, and Y. Kim, Orbitally controlled quantum Hall states in decoupled two-bilayer graphene sheets, Adv. Sci.10, 10.1002/advs.202300574 (2023)

    2023 doi

  6. [14]

    Q. Li, Y. Chen, L. Wei, H. Chen, Y. Huang, Y. Zhu, W. Zhu, D. An, J. Song, Q. Gan, Q. Zhang, K. Watanabe, T. Taniguchi, X. Shi, K. S. Novoselov, R. Wang, G. Yu, and L. Wang, Strongly coupled magneto-exciton conden- sates in large-angle twisted double bilayer graphene, Nat. Com...

    2024

  7. [15]

    Y. Cao, V. Fatemi, S. Fang, K. Watanabe, T. Taniguchi, E. Kaxiras, and P. Jarillo-Herrero, Unconventional super- conductivity in magic-angle graphene superlattices, Na- ture 556, 43–50 (2018)

    2018

  8. [16]

    Y. Cao, V. Fatemi, A. Demir, S. Fang, S. L. Tomarken, J. Y. Luo, J. D. Sanchez-Yamagishi, K. Watanabe, T. Taniguchi, E. Kaxiras, R. C. Ashoori, and P. Jarillo- Herrero, Correlated insulator behaviour at half-filling in magic-angle graphene superlattices, Nature 556, 80–84 (2018)

    2018

  9. [17]

    Yankowitz, S

    M. Yankowitz, S. Chen, H. Polshyn, Y. Zhang, K. Watan- abe, T. Taniguchi, D. Graf, A. F. Young, and C. R. Dean, Tuning superconductivity in twisted bilayer graphene, Science 363, 1059–1064 (2019)

    2019

  10. [18]

    X. Lu, P. Stepanov, W. Yang, M. Xie, M. A. Aamir, I. Das, C. Urgell, K. Watanabe, T. Taniguchi, G. Zhang, A. Bachtold, A. H. MacDonald, and D. K. Efetov, Su- perconductors, orbital magnets and correlated states in magic-angle bilayer graphene, Nature 574, 653–657 (2019)

    2019

  11. [19]

    Saito, J

    Y. Saito, J. Ge, K. Watanabe, T. Taniguchi, and A. F. Young, Independent superconductors and correlated insu- lators in twisted bilayer graphene, Nat. Phys.16, 926–930 (2020)

    2020

  12. [20]

    J. D. Sanchez-Yamagishi, T. Taychatanapat, K. Watan- abe, T. Taniguchi, A. Yacoby, and P. Jarillo-Herrero, Quantum Hall effect, screening, and layer-polarized insu- lating states in twisted bilayer graphene, Phys. Rev. Lett. 108, 076601 (2012)

    2012

  13. [21]

    Morf and B

    R. Morf and B. I. Halperin, Monte carlo evaluation of trialwavefunctionsforthefractionalquantizedHalleffect: Spherical geometry, Z. phys. B68, 391 (1987)

    1987

  14. [22]

    J. K. Jain, Composite Fermions (Cambridge University Press, Cambridge, 2007)

    2007

  15. [23]

    B. M. Hunt, J. I. A. Li, A. A. Zibrov, L. Wang, T.Taniguchi, K.Watanabe, J.Hone, C.R.Dean, M.Zale- tel, R. C. Ashoori, and A. F. Young, Direct measurement of discrete valley and orbital quantum numbers in bilayer graphene, Nat. Commun.8, 948 (2017)

    2017

  16. [24]

    I. A. McDonald and F. D. M. Haldane, Topological phase transition in the ν=2/3 quantum Hall effect, Phys. Rev. B 53, 15845 (1996)

    1996

  17. [25]

    M. R. Peterson, Y.-L. Wu, M. Cheng, M. Barkeshli, Z. Wang, and S. Das Sarma, Abelian and non-abelian states in ν = 2/3 bilayer fractional quantum Hall sys- tems, Phys. Rev. B92, 035103 (2015)

    2015

  18. [26]

    Geraedts, M

    S. Geraedts, M. P. Zaletel, Z. Papić, and R. S. K. Mong, Competing abelian and non-abelian topological orders in ν = 1/3 + 1/3 quantum Hall bilayers, Phys. Rev. B91, 205139 (2015)

    2015

  19. [27]

    W. N. Faugno, A. C. Balram, A. Wójs, and J. K. Jain, Theoretical phase diagram of two-component composite fermions in double-layer graphene, Phys. Rev. B 101, 085412 (2020)

    2020

  20. [28]

    S. C. Davenport and S. H. Simon, Spinful composite fermions in a negative effective field, Phys. Rev. B85, 245303 (2012)

    2012

  21. [29]

    Barkeshli and X.-G

    M. Barkeshli and X.-G. Wen, Non-abelian two-component fractional quantum Hall states, Phys. Rev. B82, 233301 (2010)

    2010

  22. [30]

    Read and E

    N. Read and E. Rezayi, Beyond paired quantum Hall states: Parafermions and incompressible states in the first excited landau level, Phys. Rev. B59, 8084 (1999)

    1999

  23. [31]

    Rezayi, X.-G

    E. Rezayi, X.-G. Wen, and N. Read. Condensation of fractional excitons, non-abelian states in double-layer quantum Hall systems andZ4 parafermions. Preprint at http://arxiv.org/abs/1007.2022 (2010)

    2010 arXiv

  24. [32]

    Y. Kim, A. C. Balram, T. Taniguchi, K. Watanabe, J. K. Jain, and J. H. Smet, Even denominator fractional quan- tum Hall states in higher Landau levels of graphene, Na- ture Physics 15, 154–158 (2019)

    2019

  25. [33]

    L. Wang, I. Meric, P. Y. Huang, Q. Gao, Y. Gao, H. Tran, T. Taniguchi, K. Watanabe, L. M. Campos, D. A. Muller, and others, One-dimensional electrical contact to a two- dimensional material, Science342, 614–617 (2013). Acknowledgement We thank Klaus von Klitzing, Byungmin Kang...

    2013

Pith tools

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