Cited by 171Topological Materials and PhenomenaQuantum Mechanics and Non-Hermitian PhysicsStrong Light-Matter Interactions

The DOI matches its Crossref record; 58 of the 58 references it cites were found in a registry or an index; none of the 8 sources its claims cite is checked for support yet.

Type-III and Tilted Dirac Cones Emerging from Flat Bands in Photonic Orbital Graphene

Open access
Milićević, M., Montambaux, G., Ozawa, T., Jamadi, O., Real, B., Sagnes, I., Lemaître, A., Le Gratiet, L., Harouri, A., Bloch, J., Amo, A.·2019·Physical Review X

Abstract

The extraordinary electronic properties of Dirac materials, the two-dimensional partners of Weyl semimetals, arise from the linear crossings in their band structure.When the dispersion around the Dirac points is tilted, one can predict the emergence of intricate transport phenomena such as modified Klein tunneling, intrinsic anomalous Hall effects, and ferrimagnetism.However, Dirac materials are rare, particularly with tilted Dirac cones.Recently, artificial materials whose building blocks present orbital degrees of freedom have appeared as promising candidates for the engineering of exotic Dirac dispersions.Here we take advantage of the orbital structure of photonic resonators arranged in a honeycomb lattice to implement photonic lattices with semi-Dirac, tilted, and, most interestingly, type-III Dirac cones that combine flat and linear dispersions.Type-III Dirac cones emerge from the touching of a flat and a parabolic band when synthetic photonic strain is introduced in the lattice, and they possess a nontrivial topological charge.This photonic realization provides a recipe for the synthesis of orbital Dirac matter with unconventional transport properties and, in combination with polariton nonlinearities, opens the way to study Dirac superfluids in topological landscapes.

Overview

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Written from the paper’s full text.

TL;DR

This paper demonstrates photonic orbital graphene in a honeycomb lattice of polariton micropillars, where strain in the orbital p bands produces semi-Dirac, tilted, and type-III Dirac cones. It reports the first experimental observation of type-III Dirac cones, formed by the touching of a flat band and a linear band, and explains their emergence via topological Lifshitz transitions.

Key findings

  • Type-III Dirac cones were observed for synthetic strain β = 1.5, combining a flat band and a linear band; measured velocities were |v0x| = (0.29 ± 0.03) d|tL| and |vx| = (0.35 ± 0.03) d|tL|, in agreement with tight-binding prediction |v0x| = |vx| = 0.37 d|tL|. Along the perpendicular direction, |v0y| = (0.00 ± 0.04) d|tL| and |vy| = (0.46 ± 0.04) d|tL|, matching predictions of 0 and 0.48 d|tL|.
  • A semi-Dirac dispersion was directly observed at β = 0.5, where two Dirac cones merge, with parabolic touching along ky and linear dispersion along kx.
  • Tilted type-I Dirac cones emerge from the flat-parabolic band touching at Γ for β < 1, with measured tilt v0y agreeing with tight-binding calculations.
  • Topological analysis shows the β = 1 flat-parabolic touching has winding W = 2; for β ≠ 1 it evolves into a pair of Dirac cones with W = 1, while the semi-Dirac merging has W = 0. Type-III cones are robust for 1 < β < 2 and merge at β = 2.

Methods

  • The platform is a honeycomb lattice of coupled micropillars etched from an AlGaAs semiconductor microcavity with twelve GaAs quantum wells, operating in the strong-coupling regime at 10 K to form exciton-polaritons. Micropillar diameter is 2.75 μm (2.60 μm for type-III samples), with center-to-center distances varied between 2.40 and 2.72 μm, or 2.40 and 2.10 μm for type-III.
  • Angle-resolved photoluminescence under nonresonant continuous-wave excitation at 745 nm was used to reconstruct the band dispersion. The p-orbital bands arise from coupling of first excited modes, with longitudinal hopping tL and transverse hopping tT.
  • Synthetic uniaxial strain was implemented by changing the center-to-center distance d′ along one link direction, defining β = t′L/tL. Experimental dispersions were fitted with a nearest-neighbor tight-binding model, and effective Dirac velocities were extracted from linear fits near the Dirac points.

Limitations

  • The paper states that the β = 2 merging of type-III Dirac cones could not be observed experimentally because engineered hoppings in compressed structures were limited to β = 1.5.
  • The paper notes that tT is not strictly zero in the experiment, producing faint emission between horizontal links; simulations reproduce this with tT = −0.1tL on strained links.
  • The paper states that the uppermost band deviates from a flat band due to coupling to higher-energy bands from photonic d orbitals, and that polarization-related splitting is neglected because it is much smaller than the bandwidth.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1103/physrevx.9.031010

Cites

58 of 58 references verified0 citation errors · 0 not checkable

Statistics

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Verification

Claims the paper makes

0 of 8 cited sources checked · 0 supported · 0 flagged

  • It may state two separate claims as one. 18
  • Probably not a substantial claim. 4
21 of 21
  • The paper relies on this without support.

    Type-III Dirac points have not yet been reported experimentally.

    “Type-III Dirac points have not yet been reported experimentally”
  • The authors state this as an assumption.

    In the nearest-neighbor tight-binding calculation, the coupling t_T is assumed to be zero.

    “assuming t T ¼ 0”
  • The authors state this as an assumption.

    The on-site energy for the p_x, p_y orbitals is 0.

    “where we have assumed that the on-site energy for the p x , p y orbitals is 0,”
  • The authors state this as an assumption.

    In the experiment, d ≈ d'.

    “where we have assumed that, in the experiment, d ≈ d 0”
  • The authors state this as an assumption.

    The hopping of orbitals oriented perpendicular to the links is negligible (t_T = 0).

    “If the hopping of orbitals oriented perpendicular to the links is negligible (t T ¼ 0)”
5 of 5

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Metadata

Authors
Milićević, M., Montambaux, G., Ozawa, T., Jamadi, O., Real, B., Sagnes, I., Lemaître, A., Le Gratiet, L., Harouri, A., Bloch, J., & Amo, A.
Affiliations
  • Université Paris-Sud (FR)
  • RIKEN (JP)
  • Centre National de la Recherche Scientifique (FR)
Venue
Physical Review X
Published
2019-07-23
Volume
9
Issue
3
ISSN
2160-3308 (ISSN-L)
OpenAlex
W2884840542
Cited by
171
References
55
Citations by year
2026: 8 · 2025: 27 · 2024: 28 · 2023: 22 · 2022: 27 · 2021: 30 · 2020: 25 · 2019: 4
FWCI
9.54
Type
journal article
Language
en
Open access
Locations
  • Physical Review X (publishedVersion, cc-by)
  • arXiv (Cornell University) (submittedVersion)
  • HAL (Le Centre pour la Communication Scientifique Directe) (submittedVersion, other-oa)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
  • Figshare (submittedVersion)
  • arXiv (Cornell University)
  • Greater South Information System
Funders
  • H2020 European Research Council
  • Agence Nationale de la Recherche (ANR-16-CE30-0021, ANR-11-LABX-0007, ANR-10-LABX-0035)
  • Japan Society for the Promotion of Science (JP18H05857)
  • RIKEN
  • French RENATECH network
  • CPER Photonics for Society P4S
  • I-Site ULNE
  • Métropole Européenne de Lille
Topics
  • Physical Sciences › Physics and Astronomy › Condensed Matter Physics › Topological Materials and Phenomena
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Mechanics and Non-Hermitian Physics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Strong Light-Matter Interactions
Keywords
tilted Dirac cones, flat bands, photonic lattices, honeycomb lattice, photonic resonators, topological charge, Klein tunneling, anomalous Hall effect, orbital degrees of freedom

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