colloquium, Friday, September 6, 2019, , 11:30 am Sergej Flach (Institute for Basic Science, Republic of Korea) Dynamical Glass  en route from KAM and FPUT to MBL Classical many body interacting systems are typically chaotic (nonzero Lyapunov exponents) and their microcanonical dynamics ensures that time averages and phase space averages are identical (ergodic hypothesis). In proximity to an integrable limit the long or shortrange properties of the network of nonintegrable action space perturbations define the finite time relaxation properties of the system towards Gibbs equilibrium. I will touch upon few analytical results including the KAM theorem, and review a number of computational studies which originate from the pioneering work of Enrico Fermi, John Pasta, Stanislaw Ulam and Mary Tsingou. I will then focus on short range networks which lead to a dynamical glass (DG), using a classical Josephson junction chain in the limit of large energy densities or small Josephson energies. Close to these limits the Josephson coupling between the superconducting grains induces a shortrange nonintegrable network in the corresponding action space. I will introduce a set of quantitative measures which lead to the Lyapunov time TΛ, the ergodization time TE, and to a diffusion constant D. In the DG the system fragments into large patches of nonresonant ’integrable’ grains of size l separated by triplets of resonant chaotic patches, all surviving over large times. TE sets the time scale for chaotic dynamics in the triplets. Contrary, TE ≈ l2/D is the much larger time scale of slow diffusion of chaotic triplets. The DG is a generic feature of weakly nonintegrable systems with a short range coupling network in action space, and expected to be related to nonergodic quantum metallic states of quantum manybody systems in proximity to a manybody localization phase. 
Laboratory building, room 122
Moscow Institute of Physics and Technology
Dolgoprudny, Russia
contact email address: nanotheory@phystech.edu (head M.V.Feigel'man, deputy head I.V.Zagorodnev)
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