19 research outputs found
Josephson vortex loops in nanostructured Josephson junctions
Linked and knotted vortex loops have recently received a revival of interest. Such three-dimensional topological entities have been observed in both classical- and super-fluids, as well as in optical systems. In superconductors, they remained obscure due to their instability against collapse – unless supported by inhomogeneous magnetic field. Here we reveal a new kind of vortex matter in superconductors - the Josephson vortex loops - formed and stabilized in planar junctions or layered superconductors as a result of nontrivial cutting and recombination of Josephson vortices around the barriers for their motion. Engineering latter barriers opens broad perspectives on loop manipulation and control of other possible knotted/linked/entangled vortex topologies in nanostructured superconductors. In the context of Josephson devices proposed to date, the high-frequency excitations of the Josephson loops can be utilized in future design of powerful emitters, tunable filters and waveguides of high-frequency electromagnetic radiation, thereby pushing forward the much needed Terahertz technology
Parametric amplification of vortex-antivortex pair generation in a Josephson junction
Using advanced three-dimensional simulations, we show that an Abrikosov vortex, trapped inside a cavity perpendicular to an artificial Josephson junction, can serve as a very efficient source for generation of Josephson vortex-antivortex pairs in the presence of the applied electric current. In such a case, the nucleation rate of the pairs can be tuned in a broad range by an out-of-plane ac magnetic field in a broad range of frequencies. This parametrically amplified vortex-antivortex nucleation can be considered as a macroscopic analog of the dynamic Casimir effect, where fluxon pairs mimic the photons and the ac magnetic field plays the role of the oscillating mirrors. The emerging vortex pairs in our system can be detected by the pronounced features in the measured voltage characteristics, or through the emitted electromagnetic radiation, and exhibit resonant dynamics with respect to the frequency of the applied magnetic field. Reported tunability of the Josephson oscillations can be useful for developing high-frequency emission devices
Anti-corruption policy in a socio-cultural space: indicators and actual strategies
The paper proposes a discussion of an essence, modern interpretation and directions of counteraction to corruption interaction. The paper analyzes wide (sociological) and narrow (formal-legal) approaches to the interpretation of corruption interaction, examines the causes and forms that activate the development of corruption in the post-Soviet space. The authors singled out and analyzed key aspects of the modern anticorruption policy carried out in Russia at the beginning of the 21st century. The author's vision of the content of the anti-corruption legislation is separately argued, specific proposals are formulated to improve the legislation in the conditions of an unstable legal system and a transitional state, and the basic guidelines for its further development are determined
Topological Landau-Ginzburg theory with a rational potential and the dispersionless KP hierarchy
Based on the dispersionless KP (dKP) theory, we give a comprehensive study of
the topological Landau-Ginzburg (LG) theory characterized by a rational
potential. Writing the dKP hierarchy in a general form, we find that the
hierarchy naturally includes the dispersionless (continuous) limit of Toda
hierarchy and its generalizations having finite number of primaries. Several
flat solutions of the topological LG theory are obtained in this formulation,
and are identified with those discussed by Dubrovin. We explicitly construct
gravitational descendants for all the primary fields. Giving a residue formula
for the 3-point functions of the fields, we show that these 3-point functions
satisfy the topological recursion relation. The string equation is obtained as
the generalized hodograph solutions of the dKP hierarchy, which show that all
the gravitational effects to the constitutive equations (2-point functions) can
be renormalized into the coupling constants in the small phase space.Comment: 54 pages, Plain TeX. Figure could be obtained from Kodam
Renormalization group flows and continual Lie algebras
We study the renormalization group flows of two-dimensional metrics in sigma
models and demonstrate that they provide a continual analogue of the Toda field
equations based on the infinite dimensional algebra G(d/dt;1). The resulting
Toda field equation is a non-linear generalization of the heat equation, which
is integrable in target space and shares the same dissipative properties in
time. We provide the general solution of the renormalization group flows in
terms of free fields, via Backlund transformations, and present some simple
examples that illustrate the validity of their formal power series expansion in
terms of algebraic data. We study in detail the sausage model that arises as
geometric deformation of the O(3) sigma model, and give a new interpretation to
its ultra-violet limit by gluing together two copies of Witten's
two-dimensional black hole in the asymptotic region. We also provide some new
solutions that describe the renormalization group flow of negatively curved
spaces in different patches, which look like a cane in the infra-red region.
Finally, we revisit the transition of a flat cone C/Z_n to the plane, as
another special solution, and note that tachyon condensation in closed string
theory exhibits a hidden relation to the infinite dimensional algebra G(d/dt;1)
in the regime of gravity. Its exponential growth holds the key for the
construction of conserved currents and their systematic interpretation in
string theory, but they still remain unknown.Comment: latex, 73pp including 14 eps fig