Boris Ya. Shapiro

Observation of a New Mechanism of Spontaneous Generation of Magnetic Flux in a Superconductor

We report the discovery of a new mechanism of spontaneous generation of a magnetic flux in a superconductor cooled through

Electrodynamics of type-II superconductor with periodic pinning array

{T}_{c}

Coreless vortex in p-wave superconductor

. Values of the spontaneous flux appear random from one cooldown to the next, following a Gaussian distribution. The width of the distribution increases with the size of the temperature gradient in the sample. Our observations appear inconsistent with the well-known mechanisms of flux generation. The dependence on the temperature gradient suggests that the flux may be generated through an instability of the thermoelectric superconducting-normal quasiparticle counterflow.

Effect of carbon coating on the superconducting properties of Pb and Sn nano-spheres

Abstract Static and dynamic distribution of the superconducting condensate order parameters and current density is studied by numerical simulation of the 2D time-dependent Ginzburg–Landau equations. The vortex flux lattice in layered type-II superconductors under magnetic field above the lower critical field is described by the order parameters. Moreover, the pinning effect has been considered in this work. The Abrikosov lattice which is hexagonal in the static case is deformed due to the size of pinning centers. The dynamical order parameters distribution shows that the vortex transport (flux flow) is conducted via diffusive motion of the so-called interstitial vortices. The trajectories for interstitial vortices with different sizes of pinning centers are shown.

The Vortex Core Excitation Spectrum in Gapped Topological d-wave Superconductors

Abstract We have considered coreless vortices in p-wave superconductors for arbitrary ratio κ=λ/ξ (here λ and ξ are the magnetic length and the coherence length correspondently). Both order parameter and magnetic field of the coreless vortex decaying from the vortex axis demonstrate essential difference of the vortex structure for different κ parameter and from those calculated for the vortex in liquid He3. In particular, strong asymmetry usual for some of the components of the order parameter disappears when κ parameter approaches 1.

Phase transition in vortex matter driven by bias current

Carbon coated Sn and Pb spheres of radius smaller than the superconducting coherence length of the bulk materials were fabricated using a sonochemical technique. Both samples reveal Type-I superconducting behavior characterized by supercritical fields. Analysis of the data reveal the expected enhancement of the critical field, Hc, in the Pb but not in the Sn nano-spheres. The different behavior of the Sn spheres is attributed to carbon doping which results in a decrease of their effective coherence length to below the spheres size.

Nucleation of superconductivity in an overcooled normal domain

There are indications that some high temperature unconventional superconductors have a “complex” d-wave order parameter (with an admixture of s-wave) leading to nonzero energy gap. Since the coherence length is short and the Fermi energy is relatively small the quasiclassical approach is inapplicable and the more complicated Bogoliubov-deGennes equations should be used to investigate the excitation spectrum of such a material in a magneric field. It turns out that equations for the chiral d-wave superconductor simplify considerably and is the basis for any superconductor of that type with a sufficiently large gap. The spectrum of core excitations of the Abrikosov vortex in an anisotropic 3D sample exhibits several features. Unlike in conventional and gapless superconductors the core has a single excitation mode of order energetic gap for each value of momentum along the field. This has a large impact on thermal transport and vortex dynamics.

Random telegraph voltages in high-Tc thin films at zero magnetic field

Abstract The phase transition in vortex matter subjected to external magnetic field and bias current are described by the generalized Ginzburg–Landau equations with additional convective and effective field terms. Analytical and numerical solutions of this equation provide the interface between ordered and disordered vortex phases. The location of this interface boundary depends non-monotonically on the strength of a bias current. We predict a sudden extension of the disordered vortex state across the entire sample at some critical value of the bias current.

Hot spot in type-II superconductors: dynamics and instabilities

Abstract Relaxation of the overcooled normal domain with magnetic flux in type-I and type-II superconductors is considered. Two regimes of dynamics, depending on the domain size and the amount of trapped magnetic flux have been found: decay into single vortices and explosive nucleation of the topological vortices and antivortices. Small overcooled normal spots in type-II superconductors decay into a cluster of Abrikosov vortices while the restoration of superconductivity in large domains with weak magnetic fields leads to the creation of a long-living vortex-antivortex mixed state. In the presence of pinning centers in the sample this state can be frozen and persist indefinitely. Application of a week external magnetic field extracts antivortices from the sample thus causing net increase of the magnetic penetrating into the sample.

Ginzburg - Landau theory of the triplet superconductivity in 3D Dirac semi-metal

New class of random telegraph voltage noise signals has been observed in zero field cooled BiSrCaCuO films at currents several times exceeding the critical current of the sample. The amplitude of the telegraph signal scales lienarly with current bias. Average lifetimes demonstrate distinct behavior in up and down voltage states indicating that the energy barrier associated with the down state decreases linearly with increasing current while that of the up state is nonlinear and reaches a maximum at a symmetric telegraph signal.