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Explosive growth of large-scale magnetic fluctuations due to particle scattering on developed small-scale Weibel turbulence in magnetoactive plasma

The work proposes an analytical theory of nonlinear generation of large-scale magnetic turbulence in collisionless plasma with an anisotropic velocity distribution of particle in the presence of an external magnetic field. Based on the results of the dispersion analysis of the Weibel-type instability in magnetoactive collisional plasma, and with use of the quasilinear approach, a system of equations describing the evolution of the mean-square magnetic-field energy density of small- and large-scale components of the turbulent field is obtained.

It is shown that, even in the absence of interparticle collisions, anomalous collisions of particles due to scattering on small-scale magnetic fluctuations lead to instability of long-wave harmonics, which are stable in the linear approximation. The non-linear growth of such harmonics at a given anisotropy of the particle velocity distribution, consistent with the dynamics of short-wave perturbations at the saturation stage and possible anisotropic particle injection, occurs in the superexponential regime and corresponds to an explosive-type instability (Fig. 1).

The growth law of the large-scale magnetic field is found analytically and the critical time of explosive instability is estimated. This type of fundamental plasma process is expected in a number of transient phenomena in laboratory and astrophysics, e.g., in accretion disks and jets, in stellar winds and coronal flares, in collisionless shock waves and laser ablation processes.


Fig.1 Time dependence of the mean-square magnetic-field energy density $w$. The dotted and dash-dotted lines are numerical solutions for small- and large-scale components of the turbulent field, and the blue and red solid lines are analytical solutions, respectively. A formal explosion takes place at a normalized time $\tau_c$.

 

N.Emel’yanov and V.V.Kocharovskii
JETP Letters 122, issue 2 (2025)

 

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Created by I. Podyniglazova, 2025-07-04 18:25:45
Estimation of intergranular transparency of diffusive superconducting films from the shape of the density of states of the Abrikosov vortex


This work presents a theoretical method to estimate the transparency of grain boundaries in granular superconducting films. The study is motivated by the need to better understand how grains boundary influence
the superconducting properties and vortex physics in such materials. Scanning tunneling microscopy (STM) allows high-resolution measurement of the local density of states (LDOS) in superconductors, revealing variations related
to Abrikosov vortices and grain boundaries.
Physical Picture. Vortices in thin superconducting films are strongly affected by the transparency of grain boundaries. Vortex cores can be pinned at the boundaries or inside the grains. The spatial variation of the
superconducting order parameter and LDOS around vortex cores reflects these pinning scenarios.
Theoretical Model. The film is modeled as a network of cylindrical grains with boundaries of finite transparency, characterized by a boundary resistance parameter 𝑅𝐵 . The first scenario is considered when the
vortex is located in the grain center. The Usadel equations for dirty superconductors are solved in the circular cell approximation, with appropriate boundary conditions accounting for interface transparency. Numerical Results. Calculations show that the order parameter and shielding current density exhibit sharp
jumps at grain boundaries, the magnitude of which depends on the interface transparency and the grain size. The LDOS also changes abruptly at the boundary, with the difference between LDOS values on both sides of the
interface serving as a direct measure of boundary transparency.
Experimental relevance. The approach provides a practical route to extract an information about intergranular transparency from STM measurements of the LDOS near vortices in granular films. It is shown that boundaries located several coherence lengths from the vortex center provide the most sensitive data for this estimation. The developed method offers a way to diagnose the electronic quality of grain boundaries in superconducting films, which is crucial for optimizing performance of superconducting electronics and devices. The figure shows Abrikosov vortex in a cylindrical grain (left) and the dependencies of the magnitude of the
screening current density J on the distance r from the vortex core for various grain sizes.

 

Khapaev M.M., Kupriyanov M.Yu., Golubov A.A., Stolyarov V.S.
JETP Letters 122, issue 2 (2025)

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Created by I. Podyniglazova, 2025-07-02 15:40:35
Strain-induced local nucleation of magnetic domains in iron garnet films

The magnetic bubble domains in iron garnet films, the time-honored objects of micromagnetism, have recently come into focus due to their similarity to skyrmions. It has been known for decades that the bubble domains can be induced by an external magnetic field. However, this method cannot control the number of nucleated domains and their position. Furthermore, magnetic field control relying on bulky inductive elements does not match the requirements of modern microelectronics.

In this paper the local technique for magnetic domains generation is proposed: the site of bubble domain “blowing” is determined by the contact point with the sharp tip where the strain gradient is maximum, while the size of the domain can be tuned by voltage application between the tip and sample substrate. The possibility of the combined electro-mechanical control of noncollinear spin textures is interesting in the context of straintronics and spintronics.

From the fundamental point of view this result serves as an illustration of a profound analogy between the symmetry of chiral spin structures and flexural deformation in crystals. 


 

A.P.Pyatakov et al.,
JETP Letters 122, issue 3 (2025)

 

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Created by I. Podyniglazova, 2025-06-29 23:30:17
Effects of Stark Interaction in the dynamics of an atomic system in a broadband squeezed electromagnetic field

The paper reports a derived kinetic equation describing the dynamics of an atomic localized ensemble in a broadband squeezed light field taking into account second-order effects in the constant of interaction of atoms with the field (Stark interaction). Traditionally in deriving  the kinetic equation for an open system, effects of this kind are usually ignored, but due to the established specific properties  they are considered as being "built in" and tend to renormalize  the terms of the kinetic equation determined by first-order effects.

 

The kinetic equation is derived by applying algebraic resonance perturbation theory, which defines the creating, annihilating, and counting process for a quantum stochastic differential equation. For this purpose, the Stark interaction operator of a system with a broadband quantized electromagnetic field with a nonzero photon density is represented as a quantum counting process at the stage of formation of the electromagnetic field concerned. The equation differs from the known ones, but appears to agree with them in particular and limiting cases.

 

Stark interaction manifests itself in a change in the shape of the superradiance pulse of an atomic ensemble in the Dicke state and additional shifts in the energy levels of the atom. The figure shows graphs of superradiance pulses for ensembles in the Dicke state with the same value of the number of atoms under conditions of Stark interaction with squeezed light (red graph), neglect of Stark interaction with squeezed light (blue graph), and ensemble radiation into vacuum (green graph).

 

Trubilko A.I. and Basharov A.M.
JETP Letters 122, issue 1 (2025)

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Created by I. Podyniglazova, 2025-06-24 16:19:19
First law of de Sitter thermodynamics

It is well known that there is a close connection between gravity and thermodynamics. This is especially true for the physics of black holes, whose thermodynamics is more or less generally accepted. It is determined by the temperature of the Hawking radiation from the horizon of the black hole, and the corresponding entropy is proportional to the area of the horizon, $S_{\rm BH}=A/4G$. However, in the case of the thermodynamics of the cosmological horizon in an expanding de Sitter Universe, the situation is not so clear. There are several different approaches to de Sitter thermodynamics with different assumptions about its temperature and entropy. The reason is that, unlike a black hole, the de Sitter state is not a localized object. It cannot be considered as a region bounded by the cosmological horizon. The de Sitter state is an unbounded symmetric state with constant scalar curvature.

It is usually assumed that the corresponding temperature of the de Sitter state is related to the temperature of the Hawking radiation from the cosmological horizon, the Gibbons-Hawking temperature $T_{\rm GH}=H/2\pi$, where $H$ is the Hubble parameter. However, if we consider the behavior of any object, for example an atom, placed in a de Sitter medium, it turns out that this object perceives the de Sitter vacuum as a heat bath with twice the Gibbons-Hawking temperature, $T=2T_{\rm GH}=H/\pi$. Since all points in de Sitter space are equivalent both inside and outside the horizon, this temperature is uniform, being the same for all local observers. Thus, a factor of two provides the difference between two physical temperatures: the local temperature $T$ and the temperature $T_{\rm GH}$ of the Hawking radiation from the cosmological horizon. This is one of the contradictions present in the construction of the thermodynamics of the de Sitter state.

Here we discuss the connections between these two thermodynamics, local thermodynamics and the thermodynamics of the Hubble volume, the volume of the region inside the cosmological horizon. (i) The local temperature is exactly twice the Gibbons-Hawking temperature. This connection has a simple explanation, following from de Sitter symmetry. (ii) There is a holographic connection between these thermodynamics. The entropy density integrated over the Hubble volume coincides with the entropy of the horizon, $S_{\rm Hubble}=S_{\rm horizon}=A/4G$, where $A$ is the area of the cosmological horizon. (iii) There is also a connection between the first law of local thermodynamics and the first law of global thermodynamics. Due to de Sitter symmetry, the first law is valid for an arbitrary volume $V$, which can be smaller or larger than the Hubble volume. This first law can also be applied to Hubble volume. In this case, the first law is expressed in terms of the entropy of the horizon. It is important that in both cases the thermodynamics is determined by the temperature $T=H/\pi$.

This consideration was also applied to the contracting de Sitter, for which $S_{\rm Hubble}=S_{\rm horizon}=-A/4G$. The entropy of the contracting de Sitter is negative, since its horizon is similar to the horizon of a white hole.

G.E.Volovik
JETP Letters 121, Issue 10 (2025)

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Created by I. Podyniglazova, 2025-05-02 14:44:53
Ultrafast photoluminescence and carrier localization effects in degenerate indium-rich bulk InGaN

Carrier localization in a random band potential is known to determine luminescence and lasing properties of visible-range InGaN-based light emitters. In this work, we study related effects in indium-rich InGaN ternary alloys with the near-infrared range spectral response. The investigated samples feature strong n-type residual doping inherent to InN, and we exploit this fact to perform all-optical characterization of the valence band tail states. Non-thermal hole distribution emerging at low temperatures is revealed, using time-resolved photoluminescence. A consistent model is proposed, which explains the observed strong red shift of the stimulated emission wavelength with respect to the spontaneous emission and luminescence quenching behavior at the increasing temperature.

 

K.Kudryavtsev, B.Andreev, D.Lobanov, M.Kalinnikov, A.Novikov, Z.Krasilnik
JETP Letters 121, issue 8 (2025)

 

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Created by I. Podyniglazova, 2025-04-10 17:54:21
SgrB2(N) shows a lower m_e/m_p ratio compared to Orion-KL

Fundamental physical constants are naturally included in all laws of physics. Their numerical values should reflect the properties of the world around us, but their origin remains unexplained to this day. It has been suggested since Dirac's work of 1937, 1938 that in a dynamically evolving Universe the physical constants may also be dynamical variables corresponding to the local age of the world. However, numerous laboratory experiments with various atomic and, more recently, nuclear clocks have failed to detect changes in physical constants with time at an ever deeper level, which corresponds at present to an upper limit on the relative change in, for example, the fine structure constant α, 10^(-19)/year. Astronomical spectral measurements allow such tests to go beyond laboratory experiments and study spatial and temporal constraints on variations of physical constants. It turned out that in this case the most sensitive parameter is the dimensionless quantity - the electron-to-proton mass ratio
(μ = m_e/m_p), since it determines the structure of molecular levels in a wide spectral range. The most accurate cosmological constraints, corresponding to look-back time greater than 10 billion years, give an estimate of Δμ/µ < 5*10^(-8), which is based on the analysis of methanol (CH3OH) transitions. The same order of magnitude upper limit was obtained from observations of the methanol lines in the disk of our Galaxy at relatively large galactocentric distances, R ~ 8-12 kpc.  In our work we estimated
Δμ/µ near a massive black hole, the Galactic center, at a distance R ~ 100 pc, which showed a possible decrease of μ at the level Δμ/µ = (-3.7±0.5)*10^(-7). The detected signal requires further independent study.

J.Vorotyntseva, S.Levshakov
JETP Letters 121, issue 8 (2025)

 

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Created by I. Podyniglazova, 2025-04-10 17:48:09
Cascade relaxation of the gravitating vacuum as a generator of the evolving Universe

We consider a new concept of the evolving Universe, based on the idea of many fields in the vacuum state, where their initial expectation values are zero, but the total energy density is larger than zero. We call this state the polarized vacuum in GR. The exit from this state and "rolling down'' successively in directions determined by different fields is responsible for the evolution of the Universe and can be tested through investigation of the power spectra of cosmological perturbations.

We present a model of the early Universe, which is inspired by the observational data in the spatial wavenumbers $k\in(2\cdot10^{-4}, 10)$ Mpc$^{-1}$ and does not require a solution of the Friedman equations. Based on the observations we build a solution of General Relativity in the form of vacuum attractor, which provides an additional power at $k>10\,$Mpc$^{-1}$. Extending the power spectrum to the scale of kiloparsecs and less can solve the problems of the observed cosmology --- the appearance of the early star formation and supermassive black holes at $z>10$, the birth of primordial black holes, $\Lambda$CDM model, and others.

The trajectories of the dominant field in the model of the early Universe on the phase plane ($\phi$, $\dot\phi$). Bold lines correspond to the vacuum attractor, thin lines to the general solution, and arrows indicate the time direction.

 

V.N. Lukash, E.V. Mikheeva
JETP Letters 121, issue 6 (2025)

 

 

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Created by I. Podyniglazova, 2025-03-14 15:52:04
Intrinsic anomalous Hall effect at the surface of magnetic semiconductor with strong Rashba effect

The problem of the nature of anomalous Hall effect was debated since its discovery. In magnetic topological insulators, the quantum anomalous Hall effect has been predicted and experimentally confirmed. However, in other materials with strong spin-orbit coupling, such as semiconductors with Rashba splitting, the transverse conductivity phenomenon is poorly studied.

In this letter, we theoretically investigate how electron scattering on domain walls modifies the intrinsic anomalous Hall response on the surface of a magnetic semiconductor with strong Rashba effect. The band structure of such a semiconductor, characterized by a nontrivial Berry curvature, determines the appearance of a one-dimensional resonant state on the magnetic domain wall in a local exchange gap. Under relatively weak exchange splitting, the resonant state has linear dispersion with small spectral broadening (see the figure). Moreover, it is chiral and localized near the domain wall. It is shown that the presence of a pair of parallel domain walls on the surface can have a measurable physical consequence: an additional almost half-quantized contribution to the anomalous Hall effect. The surface of the BiTeI polar semiconductor doped with transition metal atoms is a suitable material platform for experimental detection of such a contribution.

 

Spectral behavior, (a) and (b), and spatial profile (c) of electronic resonant states on the surface of the magnetic semiconductor with two parallel domain walls under varying magnetization magnitude in domains.

 

V. N. Men’shov, I. P. Rusinov, E. V. Chulkov
JETP Letters 121, issue 5 (2025)

 

 

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Created by I. Podyniglazova, 2025-02-27 18:17:32
Charge states of single quantum dots in a microcavity p-n-p heterostructure with built-in Coulomb blockade

A relatively simple method for implementing the conditions of the built-in Coulomb blockade in a quantum dot directly during the epitaxial growth of a heterostructure is proposed. This is achieved by adjusting the Fermi energy to the energy of the electron level in the quantum dot by forming a p-n-p doping profile by introducing a thin GaAs layer with n-type conductivity into the structure at a certain distance from the quantum dot layer. In this case, a neutral or charged state of an exciton in a QD can be realized without applying an external electric field, but only by varying the doping level in the n-GaAs layer and its distance to the quantum dot in accordance with the developed analytical model. Experimental studies of the spin dynamics and statistics of single-photon emission made it possible to obtain comprehensive information on the charge state of single quantum dots, the emission of which is coupled with the fundamental mode of a microcolumn microresonator. A significant increase in the probability of obtaining the required charge state for quantum dots formed using the Stranski–Krastanov growth mechanism is shown. For neutral and multiply charged quantum dots, this probability is in the range of 90-96%, and for singly charged quantum dots in the range of 70-95%. This approach represents a significant step towards complete control of optical processes in individual quantum dots for their potential application in quantum photonics.

 

A.I.Galimov, Yu.M.Serov, M.V.Rakhlin et al.,
JETP Letters 121, issue 5 (2025)

 

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Created by I. Podyniglazova, 2025-02-25 18:00:21