Cited by 509Strong Light-Matter InteractionsPlasmonic and Surface Plasmon ResearchSemiconductor Quantum Structures and Devices

Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons

Open access
Jacqmin, T., Carusotto, I., Sagnes, I., Abbarchi, M., Solnyshkov, D. D., Malpuech, G., Galopin, E., Lemaître, A. +2 more·2014·Physical Review Letters

Abstract

Two-dimensional lattices of coupled micropillars etched in a planar semiconductor microcavity offer a workbench to engineer the band structure of polaritons. We report experimental studies of honeycomb lattices where the polariton low-energy dispersion is analogous to that of electrons in graphene. Using energy-resolved photoluminescence, we directly observe Dirac cones, around which the dynamics of polaritons is described by the Dirac equation for massless particles. At higher energies, we observe p orbital bands, one of them with the nondispersive character of a flatband. The realization of this structure which holds massless, massive, and infinitely massive particles opens the route towards studies of the interplay of dispersion, interactions, and frustration in a novel and controlled environment.

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Written from the paper’s full text.

TL;DR

The paper reports direct observation of Dirac cones and a flatband in a honeycomb lattice of coupled semiconductor micropillars for polaritons. Energy-resolved photoluminescence reveals graphene-like π/π* bands with Dirac points and higher-energy P bands including a nondispersive flatband.

Key findings

  • The two lowest S bands mimic graphene’s π and π* bands, with six Dirac cones at the corners of the first Brillouin zone; a tight-binding fit gives first- and second-neighbor tunneling \(t = 0.25\) meV and \(t' = -0.02\) meV, and group velocity \(v = 3at/2\hbar = 1.3 \times 10^6\) m/s around the Dirac points.
  • Higher-energy P bands appear above the S bands, separated by \(\Delta E = 3.2\) meV between the two lowest-energy states of individual pillars; the lowest P band is flat, with an infinite effective mass, and the P bands are separated by a gap of about 0.7 meV in Fig. 1(d).
  • Increasing excitation intensity produces polariton condensation at the top of the π* band at the Γ point, with a threshold, single emission line, spatial coherence over the pump spot, and a π phase shift between adjacent pillars.
  • The flatband real-space mode has intensity maxima between pillars arranged in a kagome geometry; a tight-binding model with \(t_\parallel = -1\) meV and \(t_\perp = 0\) meV gives two flat extreme bands, while \(t_\perp = 0.2\) meV makes them dispersive, and an energy-dependent \(t_\perp\) explains the observed lower flat and upper dispersive bands.

Methods

  • Sample: a \(Q = 72000\) λ/2 microcavity with Ga\(_{0.05}\)Al\(_{0.95}\)As layer, 28 top/40 bottom Bragg mirror pairs, twelve 7 nm GaAs quantum wells, 15 meV Rabi splitting, experiments at 10 K and \(-17\) meV cavity-exciton detuning. A honeycomb lattice of coupled micropillars was etched with pillar diameter \(d = 3\) µm and lattice constant \(a = 2.4\) µm; polariton lifetime is 27 ps at the bottom of the lower polariton band, and tunnel coupling is 0.25 meV.
  • Measurements: nonresonant Ti:Sapph laser at 730 nm in a 30 µm spot covering about 30 pillars; energy-resolved photoluminescence collected through a NA = 0.65 objective, dispersed in a spectrometer, and imaged in real or momentum space with a CCD. Low-power excitation probes single-particle physics; a chopper was used at high power to avoid heating.
  • Analysis: tight-binding fits to the measured dispersion, including first- and second-neighbor tunneling; a P-state tight-binding model with \(t_\parallel\) and \(t_\perp\); supplementary 2D Schrödinger and Gross-Pitaevskii simulations.

Limitations

  • The paper states that the highest available excitation density in the experiment prevented observation of the expected modification in the spatial profile when the condensate evolves into a gap soliton.
  • Text-evident: the flatband explanation relies on a phenomenological model in which \(t_\perp\) is assumed to increase with energy, supported by numerical simulations rather than direct measurement of the energy-dependent tunneling.

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

Integrity signals

Registry

Crossref · 10.1103/physrevlett.112.116402

Cites

35 of 35 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 13 cited sources checked · 0 supported · 0 flagged

  • Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 1

    Dirac cones were directly observed in the honeycomb lattice.

    “Using energy-resolved photoluminescence we directly observe Dirac cones”
    • Also stated in: § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 2 · plain
      “We observe the six Dirac points at the corner of the first Bz (yellow points).”
    Quote in the paperSubstantial claim
  • Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 1

    A honeycomb lattice for polaritons was realized using hundreds of coupled micropillars etched in a planar semiconductor microcavity.

    “In this Letter, we report on a honeycomb lattice for polaritons, made of hundreds of coupled micropillars etched in a planar semiconductor microcavity.”
    Quote in the paperSubstantial claim
  • Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 2

    The separation between the S and P groups of bands is ΔE = 3.2 meV, the energy difference between the two lowest-energy states of the individual pillars.

    “The separation between these two groups of bands is ∆ E = 3 . 2 meV, the energy difference between the two lowest-energy states of the individual pillars.”
    Quote in the paperNot a substantial claim
  • Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 1

    The polariton condensation at the top of the π* band shows spatial coherence extended over the whole excitation spot.

    “showing spatial coherence extended over the whole excitation spot.”
    Quote in the paperNot a substantial claim
  • Findingcitation
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 2

    At higher energy, a group of four bands (P bands) arises from the coupling between the first excited state of the pillars, which is twice degenerate and has two lobes.

    “At higher energy, we observe a group of four bands ( P bands) arising from the coupling between the first excited state of the pillars, which is twice degenerate and has two lobes [22]”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [22] M. Galbiati, L. Ferrier, D. D. Solnyshkov, D. Tanese, E. Wertz, A. Amo, M. Abbarchi, P. Senellart, I. Sagnes, A. Lemaître, E. Galopin, G. Malpuech, and J. Bloch, Phys. Rev. Lett. 108 , 126403 (2012).

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims. 14
  • Classified as probably not a substantial claim. 5
  • May combine two claims.

    Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 3

    Increasing excitation intensity leads to polariton condensation, evidenced by a threshold in the integrated emission intensity.

    “By increasing the excitation intensity, we observe polariton condensation, as evidenced by the threshold in the integrated emission intensity [Fig. 3(d)].”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 1

    At higher energies, p orbital bands were observed, one of them with the non-dispersive character of a flatband.

    “At higher energies, we observe p orbital bands, one of them with the non-dispersive character of a flatband.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingreasoning
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 2

    Along line 3, emission is absent in the upper band within the first Bz, and in the lower band within the second Bz.

    “If we perform the same measurement along line 3 in Fig. 2(a), we show in Fig. 2(d) that the emission is absent in the upper band (dashed line) within the first Bz, and in the lower band (solid line) within the second Bz.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 1

    Six Dirac cones are evidenced at the corners of the first Brillouin zone, around which the energy dispersion is linear.

    “In particular, we evidence six Dirac cones at the corners of the first Brillouin zone (Bz), around which the energy dispersion is linear.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 2

    The measured energy resolved emission along lines 1 and 2 passes through four and three Dirac linear intersections respectively.

    “Figures 2(b and c) show the measured energy resolved emission along the lines 1 and 2 indicated in Fig. 2(a), passing through four and three Dirac linear intersections respectively.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 3

    At the intersection between two adjacent pillars, the fringes are shifted by half a period, indicating a π phase shift between adjacent pillars, as expected for the antibonding π* band.

    “At the intersection between two adjacent pillars [white square in Fig. 3(c)], the fringes are shifted by half a period. Thus there is a π phase shift between adjacent pillars, as expected for the antibonding π ∗ band.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingnone given
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 4

    Via resonant excitation of the structure, polariton wave packets can be created with any desired energy and momentum.

    “Moreover, via resonant excitation of the structure, polariton wave packets can be created with any desired energy and momentum.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 3

    The emission spectrum collapses into a single emission line, and extended spatial coherence builds up.

    “Moreover, the emission spectrum collapses into a single emission line, and extended spatial coherence builds up.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 3

    The real space emission of the condensate covers the same area as the pump spot.

    “The real space emission of the condensate is shown in Fig. 3(b), covering the same area as the pump spot.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingown data
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 4

    In the limiting case where t⊥ = 0 meV and t∥ = -1 meV, the eigenstates of Eq. (3) give rise to four energy bands, with the two extreme bands flat and the two intermediate ones dispersive.

    “In the limiting case where t ⊥ = 0 meV and t ‖ = -1 meV, the eigenstates of Eq. (3) give rise to four energy bands plotted in Fig. 4(c). The two extreme bands are flat, the two intermediate ones are dispersive.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingcitation
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 3

    The threshold power is similar to that observed in a planar structure.

    “The threshold power is similar to that observed in a planar structure [25].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [25] E. Wertz, L. Ferrier, D. D. Solnyshkov, P. Senellart, D. Bajoni, A. Miard, A. Lemaitre, G. Malpuech, and J. Bloch, Appl. Phys. Lett. 95 , 051108 (2009).

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Findingnone given
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 4

    The position, shape and size of each lattice site can be controlled at will during fabrication.

    “The position, shape and size of each lattice site can be controlled at will during fabrication.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Study design and conductnone given
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 2

    For low power excitation, polariton-polariton interactions are negligible so that single particle physics of the honeycomb lattice is probed.

    “Note that for low power excitation polaritonpolariton interactions are negligible so that single particle physics of the honeycomb lattice is probed.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Premisecitation
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 2

    This destructive interference occurs in lattices with multiple sites per unit cell and has been observed along the K-Γ-K' directions in angle-resolved electron spectroscopy measurements in graphene.

    “It occurs in lattices with multiple sites per unit cell [23] and has been observed along the K -Γ -K ′ directions in angle-resolved electron spectroscopy measurements in graphene [24].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [23] E.L. Shirley, L.J. Terminello, A. Santoni, and F.J. Himpsel, Phys. Rev. B 51 , 13614 (1995).

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [24] A. Bostwick, T. Ohta, T. Seyller, K. Horn, and E. Rotenberg, Nat. Phys. 3 , 36 (2006).

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Premisenone given
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 4

    The tunneling probability varies exponentially with the barrier height relative to the state, and thus increases strongly for higher energy states.

    “Indeed, the tunneling probability varies exponentially with the barrier height relative to the state, and thus increases strongly for higher energy states.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Study design and conductreasoning
    § P BANDS: 2D SCHRÖDINGER EQUATION SIMULATION · p. 7

    The 2D Schrödinger equation simulation is in excellent quantitative agreement with the experimental observation: the lowest P band is indeed flat, while the upper band is dispersive.

    “The simulation is in excellent quantitative agreement with the experimental observation: the lowest P band is indeed flat, while the upper band is dispersive.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationreasoning
    § CONDENSATION IN THE π ∗ BAND: SIMULATIONS · p. 6

    The states with negative mass are trapped in this potential and serve as a seed for stimulated scattering.

    “However, the states with negative mass are on the contrary trapped in this potential, and serve as a seed for stimulated scattering.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationcitation
    § Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons · p. 3

    The antibonding mode at the Γ point favors condensation due to its negative effective mass and positive interaction energy, and its longer lifetime.

    “The antibonding mode at the Γ point favors condensation due to two features: ( i ) its negative effective mass and positive interaction energy, ( ii ) its longer lifetime, which stems from the antisymmetric character of the state [2], and from the lower nonradiative recombination rate due to the vanishing polariton density at the constrictions between pillars, where the defect density is larger.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [2] I. L. Aleiner, B. L. Altshuler, and Y. G. Rubo, Phys. Rev. B 85 , 121301 (2012).

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

18 of 18
  • The authors state this as an assumption.

    The tunnelling probability of P states is energy dependent, increasing with energy.

    “in which we assume that the tunnelling probability is energy dependent”
    “The band structure reported in Fig. 4(a) can then be understood assuming that t ⊥ increases with the energy”
1 of 1

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • The band structure related to Dirac cones has been widely investigated in the energy-momentum space using bulk measurement with measured density and dispersion pattern.

    “The band structure related to Dirac cones has been widely investigated in the energy-momentum space using the bulk measurement with measured density and dispersion pattern [10, 22-25].”
  • The opening band gap in graphene requires large strain, even exceeding the order of 20%, attributed to deformations and anisotropy by applying strain instead of inner disorders or fluctuation.

    “One should note that the opening band gap in graphene requires large strain, even exceeding the order of 20% [24, 29], which is attributed to the deformations and anisotropy by applying strain instead of the inner disorders or fluctuation of the graphene.”

    From Observing movement of Dirac cones from single-photon dynamics (2021) · cites this paper as [24]

    The paper describes Dirac points in a polariton honeycomb lattice and compares its bands with graphene (pp. 1–2). Searches for graphene strain, a 20% threshold, and strain-induced anisotropy found no passage addressing the claimed requirement for opening a band gap or its proposed cause. (LLM, conf=0.76)

    Experimental — accuracy not yet measured

Cites

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Authors
Jacqmin, T., Carusotto, I., Sagnes, I., Abbarchi, M., Solnyshkov, D. D., Malpuech, G., Galopin, E., Lemaître, A., Bloch, J., & Amo, A.
Affiliations
  • Centre National de la Recherche Scientifique (FR)
  • University of Trento (IT)
Venue
Physical Review Letters
Published
2014-03-18
Volume
112
Issue
11
Pages
116402-116402
ISSN
  • 0031-9007 (ISSN-L)
  • 1079-7114
OpenAlex
W2043218475
Cited by
509
References
35
Citations by year
2026: 20 · 2025: 24 · 2024: 50 · 2023: 22 · 2022: 44 · 2021: 48 · 2020: 52 · 2019: 35 · 2018: 45 · 2017: 74 · 2016: 39 · 2015: 36 · 2014: 20
FWCI
27.97
Type
journal article
Language
en
Open access
Locations
  • Physical Review Letters (publishedVersion)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • HAL (Le Centre pour la Communication Scientifique Directe) (submittedVersion)
  • INO Open Portal (submittedVersion)
  • Iris (University of Trento) (submittedVersion)
  • arXiv (Cornell University)
Funders
Agence Nationale de la Recherche (ANR-11-BS10-0001, ANR-10-LABX-0035)
Topics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Strong Light-Matter Interactions
  • Physical Sciences › Engineering › Biomedical Engineering › Plasmonic and Surface Plasmon Research
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Semiconductor Quantum Structures and Devices
Keywords
polaritons, honeycomb lattice, Dirac cones, flat bands, semiconductor microcavities, graphene analogues, massless Dirac equation, band structure engineering

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