# Seminars

Regular seminars are held on Thursdays in the Kapitza Institute in Moscow and on Fridays at the scientific council of the Landau Institute in Chernogolovka.

Departments of the institute hold their own seminars; the topic are determined by the scientific orientation of the related department.

Seminars information is also sent via e-mail. If you want to receive seminar announcements, please subscribe.

## Oceanic Eddy-Induced Transport: Full-Tensor Approach

15 November in 11:30 at scientific council

Pavel S. Berloff (Imperial College London)

In geophysical turbulence effects of small-scale motions on the large-scale ones are often formulated in terms of turbulent (eddy) diffusion characterized by the eddy diffusivity coefficient. Within this context we focused on passive-tracer transport induced by mesoscale oceanic eddies and applied brute-force approach, without any simplifications and extra assumptions. The uncovered new levels of complexity of the corresponding full-tensor eddy diffusivity coefficient, referred to as the "transport tensor", call for reconsideration of how the eddy diffusion and corresponding scale interactions are treated in observations, general circulation models and theory.

## On the Novikov problem with a large number of quasiperiods and its generalizations

29 November in 11:30 at scientific council (short)

A.Ya. Maltsev

We consider the Novikov problem of describing the geometry of level lines of quasi-periodic functions on the plane. We describe here the most general case, when the number of quasi-periods of a function is not limited. The main subject of investigation is the emergence of open level lines or closed level lines of arbitrarily large sizes, which play an important role in many dynamical systems related to the general Novikov problem. As can be shown also, the results obtained for quasiperiodic functions on the plane can be generalized to the multidimensional case. In this case, we are dealing with a generalized Novikov problem, namely, the problem of describing level surfaces of quasiperiodic functions in a space of arbitrary dimension.

## Specificity of $\tau$ - approximation for chaotic electron trajectories on complex Fermi surfaces

29 November in 11:30 at scientific council (short)

A.Ya. Maltsev

We consider a special behavior of the magnetic conductivity of metals that arises when chaotic electron trajectories appear on the Fermi surface. This behavior is due to the scattering of electrons at singular points of the dynamic system describing the electron motion in the quasimomenta space, and caused by small-angle scattering of electrons on phonons. In this situation, the electronic system is described by a ``non-standard'' relaxation time, which plays the main role in a certain range of temperature and magnetic field values.

## Bound states and scattering of magnons on a superconducting vortex in ferromagnet-superconductor heterostructures

6 December in 11:30 at scientific council

__D. S. Katkov__, S. S. Apostoloff, I. S. Burmistrov

We study the magnon spectrum in a thin ferromagnetic-superconductor heterostructure in the presence of a single superconducting vortex. We employ the Bogolubov-de Gennes Hamiltonian which describes the magnons in the presence of the stray magnetic field and the non-uniform magnetic texture induced by the vortex. We find that the vortex localizes magnon states approximately in the same way as a charge center produces electron bound states due to screened Coulomb interaction in the two-dimensional electron gas. The number of these localized states is substantially determined by the material parameters of the ferromagnetic film only. We solve the scattering problem for an incident plane spin wave and compute the total and transport cross sections. We demonstrate that the vortex-induced non-uniform magnetic texture in chiral ferromagnetic film produces a skew scattering of magnons. We explore the peculiarities of the quantum scattering problem that correspond to orbiting in the classical limit.

Results are published in D.S. Katkov, S.S. Apostoloff, I. S. Burmistrov, ``Bound states and scattering of magnons on a superconducting vortex in ferromagnet-superconductor heterostructures’’, Pis'ma v ZhETF 120, 681 (2024) .(http://jetpletters.ru/ps/2486/article_36479.pdf)

Results are published in D.S. Katkov, S.S. Apostoloff, I. S. Burmistrov, ``Bound states and scattering of magnons on a superconducting vortex in ferromagnet-superconductor heterostructures’’, Pis'ma v ZhETF 120, 681 (2024) .(http://jetpletters.ru/ps/2486/article_36479.pdf)