[Landau ITP Seminars] Correction: семинары 6 сентября
Serge Krashakov
sakr at itp.ac.ru
Thu Sep 5 11:25:01 MSK 2019
В разосланном несколько минут назад письме была допущена ошибка:
В пятницу 6 октября будет заслушано 2 доклада одного и того же докладчика:
11:30 Коллоквиум
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 short-range 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 short-range 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 non-integrable systems with a short range coupling
network in action space, and expected to be related to nonergodic
quantum metallic states of quantum many-body
16:00 Семинар
Sergej Flach
*The wonderful world of flatbands*
Certain lattice wave systems in translationally invariant settings have
one or more spectral bands that are strictly flat or independent of
momentum in the tight binding approximation, arising from either
internal symmetries or fine-tuned coupling. These flat bands display
remarkable strongly interacting phases of matter. Originally considered
as a theoretical convenience useful for obtaining exact analytical
solutions of ferromagnetism, flat bands have now been observed in a
variety of settings, ranging from electronic systems to ultracold atomic
gases and photonic devices. I will review the design and implementation
of flat bands and chart future directions of this exciting field. In
particular I will focus on the field of photonic lattices. Flatband
photonic lattices consist of arrays of coupled waveguides or resonators
where the peculiar lattice geometry results in at least one completely
flat or dispersionless band in its photonic band structure. Although
bearing a strong resemblance to structural slow light, this independent
research direction is instead inspired by analogies with “frustrated”
condensed matter systems. In this talk, I will critically analyze the
research carried out to date, discuss how this exotic physics may lead
to novel photonic device applications, and chart promising future
directions in theory and experiment.
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