Effect of Cherenkov dissipation on vortex velocity in a waveguide-coupled Josephson junction

A motion of slow and fast vortices in a waveguide-coupled Josephson junction induced by a transport current flowing through the entire structure is studied; the coupling is not assumed to be weak. For a fast vortex, conditions are established under which current oscillations due to energy dissipation via Cherenkov radiation of Swihart waves become comparable to the current compensating for ohmic losses in the Josephson junction, waveguide, and adjacent superconductors. For a slow vortex, it is proved that intermediate and strong couplings of the Josephson junction to the waveguide shift current oscillations to the velocity range below the Swihart velocity of the Josephson junction.     

Vortex chains travelling with discrete velocities

It has been shown that Swihart waves slowing down caused by Josephson junction spatial dispersion leads to the new field periodic nonlinear vortex states moving with discrete velocities. Swihart waves trapping by periodic vortex structures is discovered.     

On the velocity of a 4π kink moving under the action of current

The dependence of bias current density through a junction on the velocity of a uniformly moving vortex carrying two magnetic flux quanta is established in the approximation of weakly nonlocal Josephson electrodynamics. It is shown that the velocity quantization of free motion of the vortex, which is induced by the Cherenkov interaction with Swihart waves, leads to the emergence of a discrete family of curves on the velocity-current plane.     

Cherenkov radiation from an Abrikosov-Josephson vortex

The Cherenkov radiation of generalized Swihart waves is investigated in connection with the slow motion of an Abrikosov-Josephson vortex, which corresponds to a 2 π kink in the phase difference of Cooper pairs on opposite sides of a tunnel junction. The radiative friction force acting on such a vortex is determined. An evaluation is made of the steady-state vortex velocity when the accelerating influence of an electric current through the Josephson junction is compensated by radiative slowing of the vortex due to Cherenkov radiation from the Abrikosov-Josephson vortex. Fiz. Tverd. Tela (St. Petersburg) 39, 444–448 (March 1997)     

Emission of radiation from a long Josephson junction in a thin film

Space-time nonlocal electrodynamic equations are derived for nonlinear vortex states of a Josephson junction in a film of thickness much smaller than the London penetration depth. The spectrum and damping of generalized Swihart waves propagating in such a junction are analyzed. The radiation damping constant associated with the possible emission of electromagnetic radiation is determined in the range of Swihart wave phase velocities exceeding the speed of light. The emission of radiation from nonlinear states having dimensions greater than the distance traversed by light in vacuum during the characteristic time of variation of the phase difference is investigated. It is shown that the flux density of radiation emitted by such states is localized in a plane orthogonal to the axis of the tunnel junction and depends weakly on the angle of observation in this plane. Zh. éksp. Teor. Fiz. 115, 1426–1449 (April 1999)     

Cherenkov trapping of waves and discreteness of 6 π-kink motion in a long Josephson junction

The phenomenon of Cherenkov trapping of generalized Swihart waves by a moving vortex is established using an analytically solvable model. The quantization of the structure of the field of the trapped waves is manifested as quantization of the values of the velocity of the vortices. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 4, 318–322 (25 February 1999)     

Some aspects of the nonlocal electrodynamics of infinite Josephson junctions

We derive the basic equations of nonlocal Josephson electrodynamics, valid for any ratios of the characteristic scale of phase-difference variations and junction thickness. The spectrum of generalized Swihart waves is obtained. We also study the effect of finite surface resistance of the superconducting electrodes on the dynamics of vortex structures characteristic of nonlocal electrodynamics. Zh. éksp. Teor. Fiz. 113, 955–966 (March 1998)     

On the current-voltage characteristic of a Josephson junction with a high critical current density

A theory is constructed for the current-voltage characteristic of a Josephson junction with a high critical current density described by nonlocal vortex electrodynamics in the approximation of small dissipation due to the single-particle conductivity of the Josephson junction. The role of the resonant excitation of generalized short-wavelength Swihart waves is determined. New quantitative properties of the current-voltage characteristic, which is an envelope of wave excitation resonances, are established. Zh. éksp. Teor. Fiz. 113, 2148–2161 (June 1998)     

THz Cherenkov radiation of Josephson vortex

It is shown that Josephson vortices travelling in sandwich embedded in dielectric media radiate electromagnetic waves with THz frequencies. This phenomenon is caused by the Cherenkov effect and takes place if vortex velocity exceeds the speed of light in dielectric.     

Extended Schwinger-Boson theory of the two-dimensional spin-1/2 anisotropic Heisenberg antiferromagnets

The properties of the possible solitary electromagnetic waves, propagating in two-dimensional SIS Josephson junction without dissipative losses are investigated on the basis of the local theory of the junction. A classification of the waves in the junction with respect to the Swihart velocity is made. It is shown that allowed and forbidden areas for the wave numbers, wave frequency and wave amplitude exist. The cut-off frequency for the solitary waves which velocity is greater than the Swihart velocity can be smaller than the Josephson plasma frequency and moreover these waves can propagate only in a junction that is large in the direction perpendicular to the propagation direction. On the contrary the solitary waves which velocity is smaller than the Swihart velocity request junction size in the above direction to be smaller than a critical one. The investigated two-dimensional solitary waves can be connected with one or two quanta of the magnetic flux.     

Cherenkov radiation emitted by a vortex into an anisotropic dielectric

The fields produced by a Josephson vortex moving in a sandwich placed into an anisotropic dielectric are investigated. When the vortex velocity exceeds the velocity of light in the direction of the normal to the sandwich surface, Cherenkov emission of electromagnetic waves propagating from the sandwich to the bulk of the dielectric takes place. The Poynting vector of outgoing waves is determined. It is shown that the radiation directivity considerably depends on the degree of anisotropy in the permittivity. The radiation loss power of the vortex is determined, and the relation between the transport current and the vortex velocity is established.     

On the decay of generalized Swihart waves

For Josephson junctions in sandwich geometry and in thin-film geometry we formulate the equations of nonlocal electrodynamics which take account of the influence of normal electrons in superconductors. On the basis of these equations we examine the spectrum and decay of generalized Swihart waves. We find that the decay of these waves by normal electrons becomes especially prominent in the short-wavelength region. Comparison of various dissipation mechanisms has revealed the conditions for efficient emission of electromagnetic waves from Josephson structures with finite dimensions. Fiz. Tverd. Tela (St. Petersburg) 41, 1160–1167 (July 1999)     

Vortex viscosity in magnetic superconductors due to radiation of spin waves

In type-II superconductors that contain a lattice of magnetic moments, vortices polarize the magnetic system inducing additional contributions to the vortex mass, vortex viscosity, and vortex-vortex interaction. Extra magnetic viscosity is caused by radiation of spin waves by a moving vortex. Like in the case of Cherenkov radiation, this effect has a characteristic threshold behavior and the resulting vortex viscosity may be comparable to the well-known Bardeen-Stephen contribution. The threshold behavior leads to an anomaly in the current-voltage characteristics, and a drop in dissipation for a current interval that is determined by the magnetic excitation spectrum.     

Cherenkov radiation of a Josephson vortex moving in a sandwich embedded in a dielectric medium

A motion of a Josephson vortex in a long sandwich embedded in a dielectric medium is described. If the velocity of the vortex is greater than the velocity of light in the dielectric, terahertz-band Cherenkov radiation is generated and emitted from the lateral surface of the sandwich. The radiation loss power is determined. In the case when radiation loss is compensated for by the energy gain due to transport current, a relation between the current and the velocity of the vortex is obtained.     

Whispering vortices

Experiments indicating the excitation of whispering-gallery-type electromagnetic modes by a vortex moving in an annular Josephson junction are reported. At relativistic velocities the Josephson vortex interacts with the modes of the superconducting stripline resonator giving rise to novel resonances on the current-voltage characteristic of the junction. The experimental data are in good agreement with analysis and numerical calculations based on the two-dimensional sine-Gordon model.     

Induced motion of a fast Josephson vortex

A relation is established between the transport current flowing through the entire S ₁ IS ₂ WS ₃ layered structure and the velocity of a fast vortex. The fast vortex exists when the Swihart velocity in the waveguide is significantly higher than that in the Josephson junction. It is demonstrated that the main contribution to the Lorentz force that induces the vortex motion is due to the current flowing through the waveguide and skin layers of the adjacent superconductors.