Laser thermonuclear fusion targets with calculated values of the volume and surface densities of compressed deuterium-tritium fuel of 200-300 g×cm^-³ and 1-2 g×cm^-2, respectively, are proposed for irradiating nanosecond laser pulse with an energy of 300-500 kJ, which is achievable in a modern experiment. These compression characteristics correspond to the possibility of achieving a thermonuclear gain (the ratio of the released fusion energy to the total expended energy) of 40-60 upon subsequent fast ignition with a beam of laser-accelerated protons.

The main feature of these targets is the high specific mass of deuterium-tritium fuel per unit of compressing laser pulse energy (2-3 mg×MJ^-1), which is 5-7 times greater than that of a traditional spark ignition target. In addition, the fraction of absorbed energy of the 2nd harmonic Nd laser pulse is 60-70%, which is almost 2 times more than in the case of a traditional target.

Figure shows an example of scheme of two-layer shell target for fast ignition with a fuel mass of m_DT =0.905 mg (a) and a time-dependence of corresponding laser pulse power (W_L) and the absorbed laser flux fraction δ_abs (b) for pulse  energy 500 kJ.

Fig. Typical example of two-layer shell target for fast ignition with a mass of m_DT =0.905 mg (a); time-dependence of laser pulse power (W_L) with energy 500 kJ and the absorbed laser flux fraction δ_abs (b).

S.Yu. Gus’kov, N.N. Demchenko, R.A. Yakhin
JETP Letters 123, issue 10 (2026)

Wave tunneling, one of the most basic physical phenomena, appears to be especially interesting when the wave is of vectorial nature as, for instance, the light. In particular, a vector Ginzburg-Landau equation, approximately describing quasi-monochromatic optical field in a weakly non-uniform bulk Epslilon-Near-Zero medium, predicts tunneling of specific toroidal light structures between two distant potential wells.
Each structure is a weakly dissipative transverse-electric mode with angular momentum $l=1$ for a single central-symmetric well.
In contrast, the transverse-magnetic modes, although corresponding to lower "energies", are strongly dissipative under relevant physical parameters.

The optical wave is thus characterized by two complex (pseudo)vectors ${\bf C}_{1,2}(t)$, so that each vector determines the magnitude and spatial orientation of the structure in the corresponding well. Vectors ${\bf C}_1$ and ${\bf C}_2$ are coupled by tunneling interaction, with parameters differing for components along the geometric axis and across it.

The dynamics of tunneling becomes quite non-trivial when nonlinearity is also taken into account as well as dissipative effects and external pumping. It demonstrates non-uniformly
turning tors in both wells, with the wave action flowing in a non-periodic manner from one well to the other and backward.
Direct numerical simulations of the 3D Ginzburg-Landau equation confirm qualitative predictions of approximate system of ordinary differential equations.

Fig.1a-1b:
Numerical example of two configurations of the optical field differing by the magnitudes and spatial orientations of the toroidal structures.

V. P. Ruban,
JETP Letters 123(10), (2026).

The direct comparison of the properties of X-ray emission by hot plasma of solid target, driven by nano-, pico- and femtosecond laser radiation was performed for the first time. The transition from highly uniform angular distribution of X-rays to the relatively narrow spread along the target normal and laser reflection direction was revealed at the shortening of laser pulse from nanosecond to femtosecond range. The observed result is related to the fundamental differences in the electrons energy gain mechanisms and X-rays generation process typical for laser pulses with varied duration and peak intensity. The absolute yield of broadband X-rays in the range from ~0.5 keV to a few hundreds of keV was measured, providing an insight on the conversion of laser pulse energy into high energy quanta. The observed results are important for the efficient utilization of laser-plasma sources for radiography, backlighting of ultrafast phenomena etc.

Figure. Angular distribution of X-ray dose F emitted by plasma driven by nano-, pico- and femtosecond laser pulses. 90^o corresponds to target normal.

 Bolkhovitinov E.A. et al.,
JETP Letters 123, issue 9 (2026)

Imagine a crystal where an electron, having completed a full loop in momentum space, returns not to its original state but to its mirror reflection. This is not abstract geometry, but the physical reality of the band structure predicted in our new work on heterostructures based on topological insulators.

In the paper, we propose an effective model of a layered system consisting of alternating quasi-one-dimensional strips of topological and normal insulators. The key feature of this construction is the presence of a specific non-symmorphic projective symmetry. We demonstrate that this symmetry forces the energy bands to behave as a topological Möbius surface (and in the full three-dimensional picture, as a Klein bottle).

What does this offer condensed matter physics? First, the Möbius band topology guarantees the emergence of symmetry-protected Dirac points in both gapped and gapless phases. Second, and more intriguingly, when introducing controlled dissipative effects (non-Hermiticity), this geometry gives rise to a topologically protected non-Hermitian skin effect. Unlike standard mechanisms, the localization of states at the sample edges here is dictated by the Möbius connectivity of the bands—electrons become "trapped" at the surface for fundamental symmetry reasons. This opens new avenues for controlling wave packets in real devices.

This result will be of broad interest to researchers working on topological phases, quantum geometry, and open quantum systems.

Figure 1. Schematic of the proposed heterostructure. (a) 3D visualization: a stack of quasi-1D strips shifted (step-stacked) relative to each other. Each strip consists of alternating ribbons of 2D topological (TI) and normal (NI) insulators. Intralayer ($\Delta _1, \Delta _2$) and interlayer ($\Delta $) hopping integrals between edge modes (marked with A and B) are shown (b) Side-view equivalent, illustrating the 2D periodicity. The system possesses non-symmorphic projective translation symmetry – reflection $M_x $ and a half-period shift along Z (in the basis (1,2)). Translational invariance along X is broken by dimerization (sublattices A and B). (c) Difference between mirror reflection of chiral and trivial dimers.

Z.Z. Alisultanov
JETP Letters 123, issue 9 (2026)

In altermagnets, the concept of spin-momentum locking was extended to the case of weak spin-orbit coupling. As a result, the small net magnetization is accompanied by alternating spin splitting in the k-space. Consequently, an altermagnet sometimes behaves as an antiferromagnet, and sometimes as a ferromagnet, depending on the crystal-field or interface-crystal relative orientations.

Spin-momentum locking is a key feature not only of altermagnets, but also of a large class of topological materials, where it is responsible for the spin polarization of the topological surface states. In proximity topological devices, spin-polarized surface states lead to the different realizations of the Josephson diode effect.

Experimental investigations of the Josephson current asymmetry can be conveniently performed for CrSb, which reveals both altermagnetic and topological features. Here, we experimentally investigate charge transport in In-CrSb and In-CrSb-In proximity devices, which are formed as junctions between superconducting indium leads and thick single crystal flakes of altermagnet CrSb. For double In-CrSb-In junctions, dV /dI(B) curves are mirrored in respect to zero field for two magnetic field sweep directions, which is characteristic behavior of a Josephson spin valve. Also, we demonstrate Josephson diode effect by direct measurement of the critical current for two opposite directions in external magnetic field. We interpret these observations as a joint effect of the spin-polarized topological surface states and the altermagnetic spin splitting of the bulk bands in CrSb. For a single In-CrSb interface, the superconducting gap oscillates in magnetic field for both field orientations, which strongly resembles the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) behavior. FFLO is based on finite-momentum Cooper pairing, therefore, it is fully compatible with the requirements for the Josephson diode effect.

(a) Josephson spin-valve effect as the dV /dI(B) curves reversal for two opposite magnetic field sweep directions at 30 mk temperature. The zero-resistance region is not only shifted to finite magnetic fields, but the dV /dI(B) curves are mirrored in respect to zero field,
including regions with finite resistance. (b) dV /dI(I) curves after magnetization of the sample. Differential resistance is always finite at zero field now, but there is wide zero-resistance region at 13 mT magnetic field.

Esin V.D. et.al,
JETP Letters 123, issue 8 (2026)
 

The observation of the Anomalous Hall Effect (AHE) in collinear antiferromagnets, despite their vanishing net magnetization, has been a subject of significant interest. The existence of a pseudovector that is responsible for AHE in collinear antiferromagnets is tightly connected with  the existence of the Dzyaloshinskii's invariant in the system. While all such invariants in collinear antiferromagnets have been understood for all symmetry classes, the microscopic mechanism of AHE in collinear antiferromagnets is still under research.

In this work we provide a microscopic basis for AHE in all relevant types of collinear and compensated antiferromagnets known to exhibit this effect. We show that such antiferromagnets are collinear weak ferromagnets and collinear ferrimagnets. Although, it is typical to think of weak ferromagnets as antiferromagnets with canted Néel order, in reality weak ferromagnets can have a collinear Néel order with the pseudovector consistent with the Dzyaloshinskii's invariant carried by either conducting fermions or magnons. In addition, we uncover a distinct class of ferrimagnets in which the direction of the pseudovector derived from the Dzyaloshinskii's invariant is parallel with the direction of the Néel order. The 

We show that main ingredients behind the AHE in collinear antiferromagnets are shown to be the spin-orbit coupling and spin-splitting of conducting fermions, both derived from the symmetries that allowed for the Dzyaloshinskii's invariant in the system.

There are more weak ferromagnets in Nature than the collinear antiferromagnets without the Dzyaloshinskii's invariant. Typical examples of weak ferromagnets are RuO$_2$, CrSb, CoF$_2$, NiF$_2$, $\alpha$-Fe$_2$O$_3$, MnTe, LuFeO$_3$, MnF$_2$, CoCO$_3$ and many more. Some weak ferromagnets are metallic and some insulating.

Figure 1: A minimal models of a collinear N\'{e}el ordered d-wave antiferromagnet on a square lattice, ferrimagnet on a square lattice and weak ferromagnet on rutile lattice, illustrating the magnetic (±m) and non-magnetic (green, purple and cyan) sites. This lattice geometry, along with specific symmetry breaking, underpins the emergence of AHE.

V. P. Golubinskii  and V. A. Zyuzin
JETP Letters 123, issue 5 (2026)

In quantum theory, both quantum mechanics and quantum field theory, symmetries of the action or Hamiltonian play a huge role. Symmetries can be either continuous and local, like gauge symmetry in quantum field theory, or discrete and global. In the case of quantum field theory, phase transitions occur when the parameters of the theory (temperature) change, violating the original symmetries. The properties of an effective theory in different phases turn out to be fundamentally different. The simplest example illustrating this is the 2D Ising model, in which a second-order phase transition occurs. In the high-temperature phase, the average magnetization is zero, $Z_2$ symmetry is preserved, while in the low-temperature phase, the $Z_2$ symmetry is broken and the average magnetization is nonzero.

In this paper, we study discrete quantum gravity defined on a 4D irregular lattice (simplicial complex). This theory is a mathematical model of the following physical idea: at extremely small scales, space-time exhibits granularity.

The model includes gravitational degrees of freedom as well as a Dirac fields $\Psi_{\cal V}$ and $\Psi^{\dagger}_{\cal V}$. The bare action of the theory has a global discrete $Z_4$ symmetry. The fermionic part of this action, which is bilinear relative to Dirac fields, can be rewritten in terms of effective fermionic variables $\Phi_{\cal V}$ and $\Phi^{\dagger}_{\cal V}$. These are linear combinations of the Dirac field and its conjugate at each vertex of the lattice. It can be said that the effective Dirac variables are analogous to the quasiparticle operators in superconductivity theory, constructed using Bogolyubov transformations.

A peculiarity of the construction of effective fermion operators in the lattice theory of gravity is the following fact: "particle" operators $\Phi_{\cal V}$ are invariant under $Z_4$ transformations, but their Hermitian conjugate operators $\Phi^{\dagger}_{\cal V}$ are transformed according to the simplest non-trivial representation of the group $Z_4$.

In the model under study, high-temperature expansion is correct at the highest temperatures.

As in the Ising model, it is established in this way that at the highest temperatures a $Z_4$-symmetrical phase occurs. As the temperature decreases, the $Z_4$ symmetry is broken down to its $Z_2$ symmetry subgroup. The order parameter here is the contribution to the lattice action, which transforms into the Hilbert-Einstein action in the long-wave limit. This contribution preserves $Z_2$-symmetry, but it breaks the $Z_4$-symmetry.

As the temperature decreases further, another phase transition occurs, breaking the $Z_2$-symmetry. The corresponding order parameter is a tetrad, the mean of which becomes nonzero. Spacetime emerges.

S.N. Vergeles
JETP Letters 123, issue 3 (2026)

In recent years, there has been a surge of interest in developing new approaches to improve the efficiency of existing computational methods or create fundamentally new paradigms. A particularly promising way is the shift from digital computing schemes to analog systems. One such physical system capable of emulating the structure of artificial neural networks are the diffractive neural networks. In this architecture, computation occurs passively and at the speed of light as a coherent wavefront propagates through spatially engineered diffractive layers, performing predetermined operations. However, successfully offloading computations onto an analog physical platform presents a significant challenge: it requires precise and accurate mathematical modeling that faithfully accounts for all the intricacies of the physical implementation.  Any discrepancy between the numerical model and the real-world system can lead to computational errors and degraded performance.

In this work, we directly address this challenge. We experimentally validate the correctness of our numerical modeling framework for a Fourier-diffractive neural network, in particular, we check the fidelity of using the fast Fourier transform to calculate the propagation of light in free space and its interaction with the lens and directly demonstrate the legitimacy of using the pixel of the phase mask as a weighting factor of the neural layer. Furthermore, we perform a comprehensive numerical investigation into how the exact geometry of the optical system influences the final accuracy of the computations. This study provides essential insights and design rules for bridging the gap between theoretical models and robust, high-fidelity physical mplementations of optical neural networks.

Konovalova A., Popkova A., Baluyan T., Fedyanin A.
JETP Letters 123, issue 2 (2026)