1 Breakdown of the quantum Hall effect (QHE) is commonly associated with an electric field approaching the inter Landau-level (LL) Zener field, ratio of the Landau gap and cyclotron radius. Eluded in semiconducting heterostructures, in spite of extensive investigation, the intrinsic Zener limit is reported here using high-mobility bilayer graphene and high-frequency current noise. We show that collective excitations arising from electron-electron interactions are essential. Beyond a noiseless ballistic QHE regime a large superpoissonian shot noise signals the breakdown via inter-LL scattering. The breakdown is ultimately limited by collective excitations in a regime where phonon and impurity scattering are quenched. The breakdown mechanism can be described by a Landau critical velocity as it bears strong similarities with the roton mechanism of superfluids.The Fermi sea of a 2D electronic system is unstable at high magnetic field (B-field) toward the formation of discrete Landau levels, giving rise to the quantum Hall effect (QHE) [1], where the bulk is a Landau insulator. The QHE has led to many developments in physics, including recent ones in metrology [2,3] and quantum electronics [4]. The fate of the QHE at high electric field (E-field) remains an open question, as well as the nature of the phase reached when the drift velocity v d = E × B/B 2 approaches the cyclotron velocity R c ω c , where R c and ω c are the cyclotron radius and frequency, resulting in cyclotron orbit breaking. A precursor of the transition is the quantum Hall breakdown reported soon after the discovery of QHE [5-7]. The breakdown field E bd marks the onset of longitudinal resistance and dissipation. Its natural scale is the Zener field, E c ∼hω c /eR c , with ω c =eB/m * and R c ∼ √ Nl B , where m * is the effective mass, N the number of occupied LLs and l B = h/eB the magnetic length [8]. The relevance of the Zener mechanism was soon questioned as E c exceeds experimental E bd . Besides, genuine inter-LL tunneling suffers from a strong momentum mismatch at finite doping, ∆q = 2k F where k F = √ 2N/l B is the Fermi momentum [9]. It can be circumvented assuming impurity-assisted or phonon-mediated quasi-elastic inter LL scattering (QUILLS) [8,10]. Breakdown was extensively investigated in semiconductors [6,7,11-16] and graphene [17-20], but mainly in Hall bars. Few experiments used constrictions [7,11], or Corbino geometries [21-24], with the purpose of achieving homogeneous current, or E-field, distributions. In all cases breakdown E-fields are smaller than Zener fields, and critical Hall current densities J < ∼ 50 A/m [18]. The leading explanation thus shifted to a thermal instability, driven 2 by the imbalance between dissipation and phonon relaxation [25]; its threshold is materialdependent and lower than E c [17,18,26,27]. According to low-frequency noise measurements, the thermal instability eventually gives rise to electron avalanches [11,21,22]. On comparing breakdown (v bd = J bd /ne) and Zener (v c = E c /B) velocities one ...