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Steady-state cooperative emission of interlayer excitons in atomically thin light-emitting diodes

Andrés M. Mier Valdivia, Pavel E. Dolgirev, Grace H. Chen, Nadine Leisgang, Andrew Y. Joe, Stefan Ostermann, Deepankur Thureja, Yongxin Zeng

Oct 20, 2026arXiv:2610.28304v1
cond-mat.mes-hall
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Scorecard· 16/16
7.5/10 impact

Novel demonstration of electrically driven steady-state cooperative-like emission in a 2D TMD LED with rich g2 dynamics and a quantum-optics model, at the intersection of hot fields, though the mechanism is inferred indirectly.

Abstract

When an ensemble of emitters is confined within an optical wavelength, its radiation can become correlated, leading to cooperative emission. In two-dimensional (2D) transition metal dichalcogenide (TMD) electron-hole bilayers, strong light-matter coupling enables the formation of interlayer excitons (IXs), long-lived dipolar excitations that provide an ideal setting for emergent collective phenomena. Here, we engineer an atomically thin light-emitting diode (LED) that generates electroluminescence (EL) from electrically injected IXs that are confined near the sample edges by an edge-enhanced fringing electric field. By measuring Hanbury-Brown-Twiss photon-photon correlations, we find pronounced signatures of collective decay in the form of large photon bunching followed by finite delay antibunching and bunching revivals. These emitter correlation signatures disappear when free charge carriers are doped to form a degenerate Fermi sea but are enhanced by the introduction of localized electrons. The results are consistent with a many-body quantum master equation that models the steady-state superradiant photon statistics of incoherently injected IXs. Our work establishes steady-state cooperative emission in a 2D TMD LED as a platform for studying strong light-matter interactions in electrically driven, non-equilibrium phases of Bose-Fermi mixtures.

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Impact Assessment: Steady-State Cooperative Emission of Interlayer Excitons in Atomically Thin LEDs

Core Contribution

The paper reports electroluminescence from interlayer excitons (IXs) in a dual-gated MoSe2/WSe2 heterobilayer LED whose second-order photon correlation g⁽²⁾(τ) shows features of cooperative (superradiant-like) emission. These include large bunching (g⁽²⁾(0) up to ~5 in the main data and ~13 at low current), finite-delay antibunching (~0.7), and bunching revivals on µs timescales. Emission is confined to device edges and corners by a fringing-field effect, which satisfies the sub-λ³ Dicke volume criterion. The correlations vanish when a degenerate Fermi sea is formed and are strongest when localized in-gap-state (IGS) electrons are present. A minimal three-parameter quantum master equation (N emitters, τIX, incoherent recharging time τir) reproduces the qualitative g⁽²⁾ dynamics. In the slow-recharging regime, dark subradiant states act as reservoirs that feed the bright Dicke manifold.

The novelty has three parts:

  • Steady-state cooperative emission from incoherent electrical pumping, without a cavity, in a 2D semiconductor.
  • Recharging-controlled dynamics that go beyond the standard Dicke picture.
  • A tunable electrical knob (current, gate) over the collective regime.

    • Methodological Rigor

    The device engineering is careful, using an h-BN spacer, contact gates, and scaled dual gating, and it is supported by photocurrent maps, FEM simulations, reflectance and PL characterization. The doping-regime assignments (IX⁺, IX⁰, IX⁻IGS, IX⁻) are cross-checked with several probes. Spectrally filtered g⁽²⁾ and the temperature dependence (correlations vanish at 70–80 K) add useful constraints. Consistent results are claimed across three bright spots and additional devices.

    The authors systematically rule out alternatives:

  • exciton condensation, via the emission geometry, the absence of a current anomaly, and a degeneracy-temperature estimate of ~45 K, below the 70 K at which correlations persist;
  • Mott ionization;
  • polaron beating;
  • thermal bunching;
  • cathodoluminescence-like cascades.

    • Weaknesses remain:

  • The attribution to superradiance is inferential. There is no direct measurement of the emitter number, of radiative-rate enhancement, of lifetime shortening versus density, or of g⁽¹⁾ coherence.
  • Cooperative emission requires indistinguishable emitters, yet the system has inhomogeneous broadening and the emission spans multiple peaks. The paper does not clearly show spectral indistinguishability.
  • The model is minimal and phenomenological. It ignores Coulomb interactions, Bose-Fermi physics and inhomogeneity, and it cannot explain the central doping dependence (Fermi sea suppression, localized-electron enhancement). It is fitted qualitatively with N = 25, a free parameter. It also has to explain why the oscillation period (1–5 µs) is much longer than τd.
  • Alternative classical explanations, such as blinking, charge-trap telegraph noise, or slow current fluctuations producing µs-scale bunching and anticorrelation, are not fully excluded. Bunching on µs timescales with g⁽²⁾ > 2 in electrically driven defect-rich devices could arise from charge-state switching of the IGS. The decay times are consistent with the PL lifetime, but this does not discriminate between mechanisms.
  • Data and code are only "available upon reasonable request".

    • Potential Impact

    The work is a conceptually attractive bridge between quantum optics (Dicke physics, superradiant lasers, steady-state subradiance) and 2D-material many-body optoelectronics. If the interpretation holds, it opens paths toward mirrorless 2D nanolasers, sources of non-classical or bunched light, and probes of Bose-Fermi mixtures via photon statistics. Photon correlations as a probe of many-body states in electrically tunable heterostructures could become a standard tool. Practical applications are distant: operation at 6–70 K, a few nA of current, and uncontrolled defect-based emitters.

    Timeliness

    Interest in collective emission in moiré and TMD systems is rising (cf. refs 8 and 14, which appeared recently), and so is interest in steady-state superradiance, exciton condensation controversies, and 2D nanolasers. The paper directly challenges an earlier Nature claim (ref 25) that interpreted photon bunching as evidence of condensation, so it enters an active debate. It is well positioned in time.

    Strengths

  • The first demonstration of such signatures in an electrically driven 2D heterostructure.
  • Unusually rich g⁽²⁾ dynamics (antibunching dip and revival), which are hard to mimic with simple thermal bunching.
  • Gate-tunable regimes with a clear doping dependence.
  • Combined transport, optical and simulation characterization.
  • A theoretical collaboration with a quantum optics group, giving a conceptually novel recharging/dark-state mechanism.

    • Limitations

  • The microscopic identity of the emitters is uncertain: IGS-bound, defect-localized, and ensemble size N ≈ 25 inferred indirectly.
  • The model does not capture the main doping physics.
  • The signal is demonstrated in a single material system at cryogenic temperature.
  • No direct evidence such as superlinear intensity scaling, pulsed dynamics, or coherence is provided.
  • Weak reproducibility on the data and code side.

    • Overall

    This is a high-profile, conceptually appealing experimental paper likely to attract substantial attention in 2D materials and quantum optics. Its impact will depend on whether the superradiance interpretation withstands follow-up tests. Even if the mechanism is partly revised, the platform and the electrically tunable photon-statistics measurement are likely to be reused.

    Rating:7.5/ 10
    Significance 7.5Rigor 6.5Novelty 8Clarity 7.5

    Generated Oct 21, 2026

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