arXiv subjects

E. B. Sonin

Publications and source records attributed to E. B. Sonin.

At least 19 recordsLinked to original sources

arXiv2022

Spin superfluidity

The phenomenon of superfluidity (superconductivity) is a possibility of transport of mass (charge) on macroscopical distances without essential dissipation. In magnetically ordered media with easy-plane topology of the order parameter space the superfluid transport of spin is also possible despite the absence of the strict conservation law for spin. The article addresses three key issues in the theory of spin superfluidity: topology of the order parameter space, Landau criterion for superfluidity, and decay of superfluid currents via phase slip events, in which magnetic vortices cross current streamlines. Experiments on detection of spin superfluidity are also surveyed.

cond-mat.other↗

arXiv2020

Comment on "Amplitude of waves in the Kelvin-wave cascade"

In the recently published preprint arXiv:200.02610 Eltsov and L'vov calculated the amplitudes of waves in the Kelvin-wave cascades. This returns us to the rather old, but still unresolved dispute on the role of the tilt symmetry and the locality in the Kelvin-wave cascade. The estimations by Eltsov and L'vov show that the possible nonlocality of the energy flux in the Kelvin-wave cascade has no essential effect on the Kelvin-wave cascade in the 3D vortex tangle.

cond-mat.other↗

arXiv2020

Superfluid spin transport in magnetically ordered solids

The paper reviews the theory of the long-distance spin superfluid transport in solid ferro- and antiferromagnets based on the analysis of the topology, the Landau criterion, and phase slips. Experiments reporting evidence of the existence of spin superfluidity are also overviewed.

cond-mat.other↗

arXiv2019

Interplay of spin and mass superfluidity in antiferromagnetic spin-1 BEC and bicirculation vortices

The paper investigates the coexistence and interplay of spin and mass superfluidity in the antiferromagnetic spin-1 BEC. The hydrodynamical theory describes the spin degree of freedom by the equations similar to the Landau--Lifshitz--Gilbert theory for bipartite antiferromagnetic insulator. The variables in the spin space are two subspins with absolute value $\hbar/2$, which play the role of two sublattice spins in the antiferromagnetic insulators. As well as in bipartite antiferromagnetic insulators, in the antiferromagnetic spin-1 BEC there are two spin-wave modes, one is a gapless Goldstone mode, another is gapped. The Landau criterion shows that in limit of small total spin (two subspins are nearly antiparallel) instability of supercurrents starts from the gapped mode. In the opposite limit of large total spin (two subspins are nearly parallel) the gapless modes become unstable earlier than the gapped one. Mass and spin supercurrents decay via phase slips, when vortices cross streamlines of supercurrent. The vortices participating in phase slips are nonsingular bicirculation vortices. They are characterized by two topological charges, which are winding numbers describing circulations of two angles around the vortex axis. The winding numbers can be half-integer. A particular example of a half-integer vortex is a half-quantum vortex with the superfluid velocity circulation $h/2m$. But the superfluid velocity circulation is not a topological charge, and in general the quantum of this circulation can be continuously tuned from 0 to $h/2m$.

cond-mat.other↗

arXiv2019

Superfluid spin transport in ferro- and antiferromagnets

This paper focuses on spin superfluid transport, observation of which was recently reported in antiferromagnet Cr$_2$O$_3$ [Yuan et al., Sci. Adv. 4, eaat1098 (2018)]. This paper analyzes the role of dissipation in transformation of spin current injected with incoherent magnons to a superfluid spin current near the interface where spin is injected. The Gilbert damping parameter in the Landau-Lifshitz-Gilbert theory does not describe dissipation properly, and the dissipation parameters are calculated from the Boltzmann equation for magnons scattered by defects. The two-fluid theory is developed similar to the two-fluid theory for superfluids. This theory shows that the influence of temperature variation in bulk on the superfluid spin transport (bulk Seebeck effect) is weak at low temperatures. The scenario that the results of Yuan et al. are connected with the Seebeck effect at the interface between the spin detector and the sample is also discussed. The Landau criterion for an antiferromagnet put in a magnetic field is derived from the spectrum of collective spin modes. The Landau instability starts in the gapped mode earlier than in the Goldstone gapless mode, in contrast to easy-plane ferromagnets where the Goldstone mode becomes unstable. The structure of the magnetic vortex in the geometry of the experiment is determined. The vortex core has the skyrmion structure with finite magnetization component normal to the magnetic field. This magnetization creates stray magnetic fields around the exit point of the vortex line from the sample, which can be used for experimental detection of vortices.

cond-mat.mes-hall↗

arXiv2018

Spin and mass superfluidity in ferromagnetic spin-1 Bose-Einstein condensate

The paper investigates the coexistence and interplay of spin and mass superfluidity in a ferromagnetic spin-1 Bose-Einstein condensate. Superfluidity is possible only in the presence of uniaxial anisotropy (linear and quadratic Zeeman effect). This follows from the topology of the order-parameter space (vacuum manifold). According to the Landau criterion, the critical phase gradients, both for mass and spin supercurrents, vanish at the phase transition from the easy-plane to the easy-axis anisotropy. However, mass superfluidity is still possible at the phase transition. This is because the Landau criterion signals instability only with respect to nonsingular vortices with special ratio between circulations of mass and spin currents. Phase slips produced by these vortices are not sufficient for complete decay of supercurrents. Full decay of supercurrents requires phase slips with vortices of another topological class and larger energy. These phase slips are suppressed by energetic barriers up to the upper critical velocity (gradient) exceeding the Landau critical velocity. The upper critical velocity does not vanish nor has any anomaly in the critical point at the phase transition from the easy-plane to the easy-axis anisotropy.

cond-mat.quant-gas↗

arXiv2018

Motion of vortices in ferromagnetic spin-1 BEC

The paper investigates dynamics of nonsingular vortices in a ferromagnetic spin-1 BEC, where spin and mass superfluidity coexist in the presence of uniaxial anisotropy (linear and quadratic Zeeman effect). The analysis is based on hydrodynamics following from the Gross-Pitaevskii theory. Cores of nonsingular vortices are skyrmions with charge, which is tuned by uniaxial anisotropy and can have any fractal value between 0 and 1. There are circulations of mass and spin currents around these vortices. The results are compared with the equation of vortex motion derived earlier in the Landau-Lifshitz-Gilbert theory for magnetic vortices in easy-plane ferromagnetic insulators. In the both cases the transverse gyrotropic force (analog of the Magnus force in superfluid and classical hydrodynamics) is proportional to the charge of skyrmions in vortex cores.

cond-mat.other↗

arXiv2017

Is spin superfluidity possible in YIG films?

Recently it was suggested that stationary spin supercurrents (spin superfluidity) are possible in the magnon condensate observed in yttrium-iron-garnet (YIG) magnetic films under strong external pumping. Here we analyze this suggestion. From topology of the equilibrium order parameter in YIG one must not expect energetic barriers making spin supercurrents metastable. However some small barriers of dynamical origin are possible nevertheless. The critical phase gradient (analog of the Landau critical velocity in superfluids) is proportional to intensity of the coherent spin wave (number of condensed magnons). The conclusion is that although spin superfluidity in YIG films is possible in principle, the published claim of its observation is not justified. The analysis revealed that the widely accepted spin-wave spectrum in YIG films with magnetostatic and exchange interaction required revision. This led to revision of non-linear corrections, which determine stability of the magnon condensate with and without spin supercurrents.

cond-mat.other↗

arXiv2016

Comment on "Supercurrent in a room temperature Bose-Einstein magnon condensate"

The comment explains that the preprint arXiv:1503.0042 has not presented persuasive theoretical or experimental arguments of existence of spin supercurrents in a magnon condensate prepared in a room temperature yttrium-iron-garnet magnetic film because the authors did not check known criteria for existence of spin supercurrents in magnetically ordered materials. Also they did not compare their supercurrent interpretation with a competing and more realistic scenario of transport by spin diffusion.

cond-mat.other↗

arXiv2016

Transverse forces on vortices in superfluids in a periodic potential

The paper analyzes the transverse forces (the Magnus and the Lorentz forces) on vortices in superfluids put into periodic potentials at $T=0$. The case of weak potential and the tight-binding limit described by the Bose-Hubbard model were addressed. The analysis was based on the balance of true momentum and quasimomentum. A special attention was paid to the superfluid close to the superfluid-insulator transition. In this area of the phase diagram the theory predicts the particle-hole symmetry line where the Magnus force changes sign with respect to that expected from the sign of velocity circulation. Our analysis has shown that the magnitude of the Magnus force is a continuous function at crossing the particle-hole symmetry line. This challenges the theory connecting the magnitude of the Magnus force with topological Chern numbers and predicting a jump at crossing this line. Disagreement is explained by the role of intrinsic pinning and guided vortex motion ignored in the topological approach. It is one more evidence that in general topological arguments are not sufficient for derivation of equations of vortex motion.

cond-mat.other↗

arXiv2013

Transverse force on a vortex in lattice models of superfluids

The paper derives the transverse forces (the Magnus and the Lorentz forces) in the lattice models of superfluids in the continuous approximation. The continuous approximation restores translational invariance absent in the original lattice model, but the theory is not Galilean invariant. As a result, calculation of the two transverse forces on the vortex, Magnus force and Lorentz force, requires the analysis of two balances, for the true momentum of particles in the lattice (Magnus force) and for the quasimomentum (Lorentz force) known from the Bloch theory of particles in the periodic potential. While the developed theory yields the same Lorentz force, which was well known before, a new general expression for the Magnus force was obtained. The theory demonstrates how a small Magnus force emerges in the Josephson-junction array if the particle-hole symmetry is broken. The continuous approximation for the Bose--Hubbard model close to the superfluid-insulator transition was developed, which was used for calculation of the Magnus force. The theory shows that there is an area in the phase diagram for the Bose--Hubbard model, where the Magnus force has an inverse sign with respect to that which is expected from the sign of velocity circulation.

cond-mat.other↗

arXiv2013

Tkachenko waves

This is a short review of theoretical and experimental studies of Tkachenko waves starting from their theoretical prediction by Tkachenko about 50 years ago up to their unambiguous experimental observation in the Bose--Einstein condensate of cold atoms.

cond-mat.other↗

arXiv2013

Transverse force on a vortex and vortex mass: effects of free bulk and vortex-core bound quasiparticles

The paper reassesses the old but still controversial problem of the transverse force on a vortex and the vortex mass. The transverse force from free bulk quasiparticles on the vortex, both in the Bose and the Fermi liquid, originates from the Aharonov--Bohm effect. However, in the Fermi liquid one should take into account peculiarities of the Aharonov--Bohm effect for BCS quasiparticles described by two-component spinor wave functions. There is no connection between the transverse force (either from free bulk quasiparticles or from vortex-core bound quasiparticles) and the spectral flow in the vortex core in superfluid Fermi liquid, in contrast to widely known claims. In fact, there is no steady spectral flow in the core of the moving vortex, and the analogy with the Andreev bound states in the SNS junction, where the spectral flow is really possible, is not valid in this respect. The role of the backflow on the vortex mass is clarified. The backflow is an inevitable consequence of a mismatch between the currents inside and outside the vortex core and restores the conservation of the particle number (charge) violated by this mismatch. In the Fermi liquid the backflow compensates the current through the core bound states, which is a source of the vortex mass (the Kopnin mass). This results in renormalization of the Kopnin vortex mass by a numerical factor.

cond-mat.other↗

arXiv2012

Spin superfluidity, coherent spin precession, and magnon BEC

Spin superfluidity, coherent spin precession, and magnon BEC are intensively investigated theoretically and experimentally nowadays. Meanwhile, clear definition and differentiation between these related phenomena is needed. It is argued that spin stiffness, which leads to existence of coherent spin precession and dissipationless spin supercurrents, is a necessary but not sufficient condition for spin superfluidity. The latter is defined as a possibility of spin transport on macroscopical distances with sufficiently large spin supercurrents. This possibility is realized at special topology of the magnetic-order-parameter space, such as, e.g., that in easy-plane antiferromagnets. It is argued that an arbitrarily chosen formal criterion for the existence of magnon BEC has no connection with conditions for observation of macroscopic dissipationless spin transport.

cond-mat.other↗

arXiv2012

Reply to Comment on "Symmetry of Kelvin-wave dynamics and the Kelvin-wave cascade in the T=0 superfluid turbulence" [arXiv:1208.4593]

I discuss the Comment by L'vov and Nazarenko (arXiv:1208.4593) aiming at refutation of my perviously published criticism of their mechanism of the Kelvin-wave cascade. It is important that in their Comment L'vov and Nazarenko admitted that the Hamiltonian, from which they derived their mechanism, is not tilt-invariant. This provides full ammunition to their critics, who believe that their mechanism is in conflict with tilt symmetry of the Kelvin-wave dynamics in an isotropic space.

cond-mat.other↗

arXiv2012

Symmetry of Kelvin-wave dynamics and the Kelvin-wave cascade in the T=0 superfluid turbulence

The article considers implications of tilt symmetry (symmetry with respect to tilting of the coordinate axis with respect to which vortex motion is studied) in the non-linear dynamics of Kelvin waves. The conclusion is that although the spectrum of Kelvin wave is not tilt-invariant, this does not compromise tilt invariance of the Kelvin-wave cascade vividly argued now in the theory of superfluid turbulence. The article investigates the effect of strong kelvon interaction on the power-law exponent for the Kelvin-wave cascade and suggests a simple picture of the crossover from the classical Kolmogorov cascade to the quantum Kelvin-wave cascade, which does not encounter with mismatch of the energy distributions at the crossover and does not require a broad intermediate interval for realization of the crossover.

cond-mat.other↗

arXiv2011

Dynamics of helical vortices and helical-vortex rings

The Letter considers dynamics of helical vortices and helical-vortex rings either solving directly the equations of motions of a vortex line or using canonical relations following from the Hamiltonian equations of motion. An analytical solution in elliptical integrals was found for helical-vortex rings in the local-induction approximation. The analysis based on the canonical Hamilton relation provides a clear physical explanation for anomalous velocities of helical-vortex rings, i.e., for suppression of the velocity and even inversion of its direction at sufficiently large amplitude of the helical distortion. The extended local-induction approximation is suggested, which provides an exact solution for the equations of motion of helical vortices and helical-vortex rings in the limit when the small-pitch helical vortex reduces to a cylindric sheet of uniform vorticity.

cond-mat.other↗

arXiv2011

Dynamics of twisted vortex bundles and laminar propagation of the vortex front

The paper is studying the dynamics of twisted vortex bundles, which were detected in experimental investigations of superfluid turbulence in superfluid 3He-B. The analysis shows that a linear torsion oscillation of a vortex bundle is a particular case of the slow vortex mode related with the inertial wave, which was already investigated in the past in connection with observation of the Tkachenko waves in superfluid 4He and the experiments on the slow vortex relaxation in superfluid 3He-B. The paper addresses also a twisted vortex bundle terminating at a lateral wall of a container starting from the elementary case when the bundle reduces to a single vortex. The theory considers the laminar regime of the vortex-bundle evolution and investigates the Glaberson-Johnson-Ostermeier instability of the laminar regime, which is a precursor for the transition to the turbulent regime at strong twist of the bundle. The propagation and the rotation velocities of the vortex front (the segment of the vortex bundle diverging to the wall) can be found from the equations of balance for the linear and the angular momenta, and the energy. It is demonstrated that the vortex front can move with finite velocity even in the absence of mutual friction (the T = 0 limit). The theory is compared with experimental results on vortex-front propagation in superfluid 3He-B.

cond-mat.other↗