Russian Academy of Sciences

Landau Institute for Theoretical Physics

In Print

Embossing of silicon with an ultrashort laser pulse diffracted by a bubble in liquid

17 March in 11:30 (short)

N.A. Inogamov

Laser-assisted nanostructuring of silicon interfaces provides a unique procedure for leading-edge technologies. We report on a new embossing technique with tightly focused Gaussian-shaped ultrashort laser pulses near the ablation threshold in liquid. We take advantage of a primary microbubble for controllable spatial-modulation of light intensity of succeeding pulses. Such a bubble, generated in liquid near the molten silicon surface by the first pulse, serves as an obstacle for the second pulse following with a sub-millisecond time delay, to produce a diffraction ring pattern. Variation of laser intensity can be utilized to guide the diffraction patterns. Thus the various annular patterns deeply embossed up to hundreds nanometers on the surface are produced with high reproducibility. Morphology of modified surface layer is investigated in detail using atomic-force microscopy, as well as scanning and transmission electron microscopies. Full-wave EM modeling of laser beam diffraction by the bubbles with various radii and shapes shows that the peak intensity in silicon is up to 1.7 times higher than in bubble-free liquid. Atomistic simulation of ultrafast heating with such a diffraction peak reveals that an annular microdimple surrounded by rims is formed by high-gradient pressure in molten silicon to be frozen after several nanoseconds.
S.A. Romashevskiy, A.I. Ignatov, V.V. Zhakhovsky, E.M. Eganova, E.A. Pershina, N.A. Inogamov, S.I. Ashitkov, Embossing of silicon with an ultrashort laser pulse diffracted by a bubble in liquid, Applied Surface Science, 615, 156212 (2023)

Improving of ultracold neutrons traps coated with a liquid helium film by an electrostatic potential

10 March in 11:30 (short)

P.D. Grigoriev, A.V. Sadovnikov, V.D. Kochev, A.M. Dyugaev

It is shown that applying an electric voltage to the rough walls of ultracold neutron trap covered with liquid helium increases the thickness of liquid He and additionally protect UCN from being absorbed in the trap walls. The estimates of the required intensity of the electric field show that it is realizable. The possibility of the influence of the electric field on the dispersion law of surface waves, which lead to UCN losses in the trap due to their inelastic scattering by riplons, is studied.
The paper is available at

Bound pairs of "magnetic skyrmion – superconducting vortex" in thin bilayers

20 January in 11:30

S. Apostoloff, E. Andriaykhina, P. Vorobyev, O. Tretiakov, I. Burmistrov

In a recent paper [Phys. Rev. B 103, 174519 (2021)] it has been theoretically shown that a Néel magnetic skyrmion and a superconducting Pearl vortex can form bound pairs in bilayers of the superconductor and ferromagnetic thin films due to the stray fields. Depending on the parameters of the system, the centers of the skyrmion and the vortex can be located either strictly above each other or at a finite distance of the order of the skyrmion radius. However, the analysis in that paper was limited to the main order of the perturbation theory in the magnetic field of the vortex. The report will present a more detailed study of such bound pairs in systems in which stabilization of the skyrmion is determined by the Dzyaloshinskii–Moriya interaction. Firstly, it will be shown that with an increase in the effective strength of the vortex, a counterintuitive phenomenon occurs: the repulsion between the skyrmion and the vortex is suppressed, and the distance between their centers decreases [JETP Letters, 116(11), 801-807 (2022) / arXiv:2210.08790]. Secondly, for the coaxial skyrmion and vortex, a significant change of the skyrmion is predicted: the chirality can change and/or the radius can increase significantly. In addition, with the same heterostructure parameters, but depending on the initial magnetization distribution in a ferromagnet, up to three different bound pairs of "skyrmion – vortex" can arise, where one skyrmion has negative chirality, and the other two have different radii and positive chirality [arXiv:2212.08351 / submitted to PRL].

Comment on "Super-universality in Anderson localization"

30 December 2022 in 11:30 (short)

I.S. Burmistrov

Comment on recent paper by I. Horváth and P. Markoš, "Super-universality in Anderson localization", Phys. Rev. Lett. 129, 106601 (2022) [arXiv:2110.11266]
Details can be found in arXiv:2210.10539

The first signal of jet quenching in pp collisions

23 December 2022 in 11:30 (short)

B.G. Zakharov

We discuss jet quenching in mini quark-gluon plasma produced in $pp$ collisions. We study the modification factor $I_{pp}$, describing the medium modification of the jet fragmentation functions. We calculate $I_{pp}$ within the light-cone path integral approach to induced gluon emission for parametrization of the running coupling $\alpha_s(Q,T)$ which has a plateau around $Q=\kappa T$, motivated by the lattice calculations of the effective QCD coupling in the quark-gluon plasma. We calculate $I_{pp}$ with no free parameters using $\kappa$ fitted to the LHC data on the nuclear modification factor $R_{AA}$. We find that the predicted decrease with multiplicity of $I_{pp}$ for $5.02$ TeV $pp$ collisions agrees reasonably with the recent preliminary data from ALICE. Our results show that the drop of $I_{pp}$ with the multiplicity, if confirmed by further measurements, may be viewed as the first direct evidence for jet quenching in $pp$ collisions.

Interplay of superconductivity and localization near a 2D ferromagnetic quantum critical point

23 December 2022 in 11:30

P.A. Nosov, I.S. Burmistrov, S. Raghu

We study the superconducting instability of a two-dimensional disordered Fermi liquid weakly coupled to the soft fluctuations associated with proximity to an Ising-ferromagnetic quantum critical point. We derive interaction-induced corrections to the Usadel equation governing the superconducting gap function, and show that diffusion and localization effects drastically modify the interplay between fermionic incoherence and strong pairing interactions. In particular, we obtain the phase diagram, and demonstrate that: (i) there is an intermediate range of disorder strength where superconductivity is enhanced, eventually followed by a tendency towards the superconductor-insulator transition at stronger disorder; and (ii) diffusive particle-particle modes (so-called `Cooperons') acquire anomalous dynamical scaling z=4, indicating strong non-Fermi liquid behaviour.

Long-range interactions between membrane inclusions: Electric field induced giant amplification of the pairwise potential

16 December 2022 in 11:30

E.S. Pikina, A.R. Muratov, E.I. Kats, V.V. Lebedev

The aim of this work is to revisit the phenomenological theory of the interaction between membrane inclusions, mediated by the membrane fluctuations. We consider the case where the inclusions are separated by distances larger than their characteristic size. Within our macroscopic approach a physical nature of such inclusions is not essential. However, we have always in mind two prototypes of such inclusions: proteins and RNA macromolecules. Because the interaction is driven by the membrane fluctuations and the coupling between inclusions and the membrane, it is possible to change the interaction potential by external actions affecting these factors. As an example of such external action we consider an electric field. Under external electric field (both dc or ac), we propose a new coupling mechanism between inclusions possessing dipole moments (as it is the case for most protein macromolecules) and the membrane. We found, quite unexpected and presumably for the first time, that the new coupling mechanism yields to giant enhancement of the pairwise potential of the inclusions. This result opens up a way to handle purposefully the interaction energy, and as well to test of the theory set forth in our article.
Results are published in Annals of Physics 447(Pt.2), 168916 (2022);

The structure of angular diagrams for systems describing the dynamics of an electron in a magnetic field for dispersion laws in general position

16 December 2022 in 11:30 (short)

I.A. Dynnikov, A.Ya. Maltsev, S.P. Novikov

We present a number of results that significantly refine the description of the angular diagrams that arise in the study of the dynamics of an electron in a magnetic field at all energy levels simultaneously. The description allows us to introduce some hierarchical structure on the set of stability zones on such diagrams, as well as to describe in more detail the set of occurrence of complex (chaotic) trajectories of the corresponding dynamical system. ZhETF, Volume 162, Issue. 2 (2022), UMN, volume 77, issue 6(468) (2022)

Open level lines of a superposition of periodic potentials on a plane

16 December 2022 in 11:30 (short)

A.Ya. Maltsev, S.P. Novikov

We study the geometry of open potential level lines arising from the superposition of two different periodic potentials on a plane. This problem can be considered as a particular case of the Novikov problem on the behavior of open level lines of quasi-periodic potentials on a plane with four quasi-periods. At the same time, the formulation of this problem can have many additional features. We will give a general description of the emerging picture both in the most general case and in the presence of additional restrictions. The main approach to describing the behavior of open level lines is based on their division into topologically regular and chaotic level lines. Annals of Physics, In Press, Corrected Proof, Available online 22 July 2022, art. 169039; arXiv:2206.04014

NSR singular vectors from Uglov polynomials

9 December 2022 in 11:30 (short)

Mikhail Bershtein

It was conjectured in 2012 that bosonization of a singular vector (in the Neveu–Schwarz sector) of the N=1 super analog of the Virasoro algebra can be identified with the Uglov symmetric function. We prove this conjecture. We also extend this result to the Ramond sector of the N=1 super-Virasoro algebra.
Based on joint work: M. Bershtein, A. Vargulevich, "NSR singular vectors from Uglov polynomials", J. Math. Phys. 63, 061706 (2022), arXiv:2202.11810.

Semiclassical approach to calculation of form factors in the sinh-Gordon model

2 December 2022 in 11:30

M. Lashkevich, O. Lisovyy, T. Ushakova

Form factors in the sinh-Gordon model are studied semiclassically for small values of the parameter $b$ on the background of a radial symmetric classical solution. For this purpose we use a generalization of the radial quantization, well known for a massless boson field. We obtain new special functions, which generalize the Bessel functions and have an interesting interpretation in the theory of the classical sinh-Gordon model. The form factors of the exponential operators are completely determined by classical solutions in the leading order, while the form factors of descendant operators contain quantum corrections even in the leading order. Consideration of descendant operators in two chiralities demands renormalizations, which are analogous to those in the conformal perturbation theory.

Bogoyavlensky lattices and the generalized Catalan numbers

2 December 2022 in 11:30 (short)

V.E. Adler

Several years ago A.B. Shabat proposed the problem on the decay of the unit step solution for the Volterra lattice terminated on a half-line. It is resembling the Gurevich-Pitaevsky problem on the step-like solutions for the KdV equation, but it turned out to be simpler since the answer is found explicitly. One solution method is based on the observation that the Taylor series for the tau function of the lattice equation serves as the exponential generating function for the Catalan numbers and is expressed in terms of a hypergeometric function. This can be proved using the well-known result in combinatorics that the Hankel transform for the Catalan numbers is the identity sequence. The second method uses a finite-dimensional reduction associated with the master-symmetry of the lattice; the solution with the unit step initial data is contained within this reduction. This talk is about similar results on the relations between the Bogoyavlensky lattices, the generalized Catalan numbers (known in combinatorics) and the generalized hypergeometric functions.