One of the relevant tasks in modern hydrodynamics is the study of quantum turbulence, as well as the mechanisms of formation and decay of quantum vortices in quantum liquids and gases. Quantum vortices in superfluid helium‑4 are topological defects that must begin and end on the surface of the liquid or on the walls of the container [1], or they can form closed loops in the bulk [2]. The principal difference from classical vortices is the quantization of the flow circulation around the vortex core, with the circulation quantum being equal to $h/m_{He}$ , where  is the Planck constant and $m_{He}$ is the mass of a helium‑4 atom.

Recent theoretical and experimental studies of the nonlinear interaction between waves propagating on the surface of a classical viscous fluid (for example, water) have demonstrated that the surface waves’ interaction can lead to the generation of vortex flows on the surface of a viscous fluid [3]. The features of vortex flow generation by waves on the surface of a quantum fluid, where normal and superfluid helium coexist simultaneously, had not been previously investigated theoretically. As our experiments [4] have shown, when the wave amplitudes exceed critical values, waves on the surface of He‑II can excite not only classical vortices in the normal helium but also quantum vortices under the surface of the liquid layer.

This work is devoted to studying the penetration depth of quantum vortices, which are formed during the nonlinear interaction of two mutually orthogonal capillary waves on the surface of the He‑II layer, into the liquid bulk at temperatures  $T $ = 1.5 and 1.7 K. To detect the excitation of quantum vortices, negative charges (“electron bubbles” with a radius of 17 Å) were injected into liquid helium were used as tracer particles, which can be captured by quantum vortices at liquid temperatures below 1.7 K. It has been established that the quantum vortices generated by capillary waves with a frequency of $ f = 49.9 $ Hz are concentrated under the liquid surface in a narrow layer less than 50 nm deep, which is much less than the depth of the viscous sublayer of normal helium,  $\delta \sim 5 μm$.

[1] P. Moroshkin, P. Leiderer, K. Kono, S. Inui and M. Tsubota, "Dynamics of the Vortex-Particle Complexes Bound to the Free Surface of Superfluid Helium", Phys. Rev. Lett. 122, 174502 (2019);

[2] P. M. Walmsley, A. I. Golov, H. E. Hall, A. A. Levchenko and W. F. Vinen, "Dissipation of Quantum Turbulence in the Zero Temperature Limit", Phys. Rev. Lett. 99, 265302 (2007);

[3] S. S. Vergeles, A. A. Levchenko and V. M. Parfenyev, "Nonlinear generation of currents by waves on liquid surface", Phys. Usp. 68, 1131 (2025);

[4] P. G. Selin, I. A. Remizov, M. R. Sultanova, E. V. Lebedeva, A. A. Levchenko and L. P. Mezhov-Deglin, "Threshold of Generation of Quantum Vortices by Waves on the Surface of Superfluid He-II", JETP Lett. 122, 178 (2025).

 

I.A. Remizov, P.G. Selin, E.V. Lebedeva et al.
JETP Letters 124, issue 8 (2026)

 

 

This work is motivated by recent experiments of V. V. Dmitriev's group, which investigated the effect of impurity magnetic scattering on the properties of the superfluid phases of ³He [1,2]. The experiments showed that the temperature range of the stable polar phase of superfluid ³He in a nematic aerogel vanishes when a small amount of solid paramagnetic ³He is present on the aerogel surface. In this case, a chiral polar-distorted A-phase with a finite degree of distortion emerges directly from the normal state instead of the axially symmetric polar phase.

We propose a microscopic mechanism for this instability based on the emergence of an effective spin-orbit interaction as quasiparticles scatter off the spatially inhomogeneous magnetic texture of the solid layer. Due to the finite curvature and roughness of the aerogel strands, a Berry curvature field is induced via magnetic correlations, lying primarily in the plane perpendicular to the anisotropy axis of aerogel. This interaction simultaneously breaks both the axial symmetry and the time-reversal invariance, which is essential for the observed effect.

Within Gorkov's equations in the p-wave channel, this double symmetry breaking introduces imaginary non-diagonal terms into the self-consistency matrix. Consequently, the pure polar phase no longer maximizes the transition temperature, yielding to the polar-distorted A-phase. In the limit where the interaction under consideration is strong enough, that is, when the non-diagonal elements of the perturbation matrix dominate over the difference between the diagonal ones, the solution approaches the form of the pure A-phase.

 

1. V. V. Dmitriev, A. A. Soldatov, A. N. Yudin, "Effect of Magnetic Boundary Conditions on Superfluid ³He in Nematic Aerogel", Phys. Rev. Lett., 120, 075301 (2018)
2. V. V. Dmitriev, D. V. Petrova, A. A. Soldatov, A. N. Yudin, “The effect of pressure on the splitting of the superfluid transition in ³He in nematic aerogel”, Pis’ma v ZhETF, 124,  216 (2026)
   
   
    

Evgeny Surovtsev
JETP Letters 124, issue 7 (2026)

Quantization of the circulation of a magnon supercurrent was observed in a closed loop of yttrium-iron garnet film. Due to the low mass of magnons and their gaseous state at high concentrations, it was possible to obtain a magnon Bose-Einstein condensate at room temperature. [1].   According to the theory, the transition of magnons to a BEC state occurs when the precessing magnetization deviates by more than 2.5 degrees [2].    This phase transition has been experimentally observed precisely at this magnon concentration [3].  States with 2π and 4π circulation were observed. These states exhibit high stability. The circulation number is conserved under various changes in the phase difference of the radio-frequency pumping. It can be changed only by destroying and restoring the BEC with a new phase distribution. Thus, the magnon BEC possesses properties typical of the superfluid state! It should be noted that the kinematics of a magnon BEC is not described by the quasiclassical Landau-Lifshitz equations [1].  We also succeeded in creating a permanent magnon BEC using the method of auto-generation [4]. Thus, the magnon BEC represents a new platform for the development of quantum technologies at room temperature.

Fig.1. The phase shift of magnetization precession 4π along the YIG film ring

 

[1] G. A. Knyazev, A. N. Kuzmichev, P. E. Petrov, I. V. Savochkin, P. M. Vetoshko, V. I. Belotelov, and Yu. M. Bunkov, Optics Express 32, 13761-13768 (2024)
        [2] Yu. M. Bunkov, V. L. Safonov, J. Mag. Mag. Mat., 452,30–34 (2018)
        [3] P. E. Petrov, G. A. Knyazev, A. N. Kuzmichev, P. M. Vetoshko, V. I. Belotelov, and Yu. M. Bunkov, JETP Letters 119, 118 – 122 (2024).
        [4]. Yu. M. Bunkov, P. M. Vetoshko, G. A. Knyazev, A. N. Kuzmichev, D. A. Samodelkin, JETP Letters 123, 119-123, (2026).

Bunkov Yu. et al.,
JETP Letters 124, issue 7 (2026)

 

 

 

Quantization of the circulation of a magnon supercurrent was observed in a closed loop of yttrium-iron garnet film. Due to the low mass of magnons and their gaseous state at high concentrations, it was possible to obtain a magnon Bose-Einstein condensate at room temperature. [1].   According to the theory, the transition of magnons to a BEC state occurs when the precessing magnetization deviates by more than 2.5 degrees [2].    This phase transition has been experimentally observed precisely at this magnon concentration [3].  States with 2π and 4π circulation were observed. These states exhibit high stability. The circulation number is conserved under various changes in the phase difference of the radio-frequency pumping. It can be changed only by destroying and restoring the BEC with a new phase distribution. Thus, the magnon BEC possesses properties typical of the superfluid state! It should be noted that the kinematics of a magnon BEC is not described by the quasiclassical Landau-Lifshitz equations [1].  We also succeeded in creating a permanent magnon BEC using the method of auto-generation [4]. Thus, the magnon BEC represents a new platform for the development of quantum technologies at room temperature.