Triode for Magnetic Flux Quanta

In an electronic triode, the electron current emanating from the cathode is regulated by the electric potential on a grid between the cathode and the anode. Here we demonstrate a triode for single quantum magnetic field carriers, where the flow of individual magnetic vortices in a superconducting film is regulated by the magnetic potential of striae of soft magnetic strips deposited on the film surface. By rotating an applied in-plane field, the magnetic strip potential can be varied due to changes in the magnetic charges at the strip edges, allowing accelerated or retarded motion of magnetic vortices inside the superconductor. Scaling down our design and reducing the gap width between the magnetic stripes will enable controlled manipulation of individual vortices and creation of single flux quantum circuitry for novel high-speed low-power superconducting electronics

Faraday rotation spectra of bismuth-substituted ferrite garnet films with in-plane magnetization

Single crystalline films of bismuth-substituted ferrite garnets have been synthesized by the liquid phase epitaxy method where GGG substrates are dipped into the flux. The growth parameters are controlled to obtain films with in-plane magnetization and virtually no domain activity, which makes them excellently suited for magnetooptic imaging. The Faraday rotation spectra were measured across the visible range of wavelengths. To interprete the spectra we present a simple model based on the existence of two optical transitions of diamagnetic character, one tetrahedral and one octahedral. We find excellent agreement between the model and our experimental results for photon energies between 1.77 and 2.53 eV, corresponding to wavelengths between 700 and 490 nm. It is shown that the Faraday rotation changes significantly with the amount of substituted gallium and bismuth. Furthermore, the experimental results suggest that the magnetooptic response changes linearly with the bismuth substitution.Comment: 15 pages, 6 figures, published in Phys. Rev.

Strong 3D correlations in vortex system of Bi2212:Pb

The experimental study of magnetic flux penetration under crossed magnetic fields in Bi2212:Pb single crystal performed by magnetooptic technique (MO) reveals remarkable field penetration pattern alteration (flux configuration change) and superconducting current anisotropy enhancement by the in-plane field. The anisotropy increases with the temperature rise up to $T_m = 54 \pm 2 K$. At $T = T_m$ an abrupt change in the flux behavior is found; the correlation between the in-plane magnetic field and the out-of-plane magnetic flux penetration disappears. No correlation is observed for $T > T_m$. The transition temperature $T_m$ does not depend on the magnetic field strength. The observed flux penetration anisotropy is considered as an evidence of a strong 3D - correlation between pancake vortices in different CuO planes at $T < T_m$. This enables understanding of a remarkable pinning observed in Bi2212:Pb at low temperatures.Comment: 8 pages, 9 figure

Josephson vortices and solitons inside pancake vortex lattice in layered superconductors

In very anisotropic layered superconductors a tilted magnetic field generates crossing vortex lattices of pancake and Josephson vortices (JVs). We study the properties of an isolated JV in the lattice of pancake vortices. JV induces deformations in the pancake vortex crystal, which, in turn, substantially modify the JV structure. The phase field of the JV is composed of two types of phase deformations: the regular phase and vortex phase. The phase deformations with smaller stiffness dominate. The contribution from the vortex phase smoothly takes over with increasing magnetic field. We find that the structure of the cores experiences a smooth yet qualitative evolution with decrease of the anisotropy. At large anisotropies pancakes have only small deformations with respect to position of the ideal crystal while at smaller anisotropies the pancake stacks in the central row smoothly transfer between the neighboring lattice positions forming a solitonlike structure. We also find that even at high anisotropies pancake vortices strongly pin JVs and strongly increase their viscous friction.Comment: 22 pages, 11 figures, to appear in Phys. Rev.

Dynamic Vortex Phases and Pinning in Superconductors with Twin Boundaries

We investigate the pinning and driven dynamics of vortices interacting with twin boundaries using large scale molecular dynamics simulations on samples with near one million pinning sites. For low applied driving forces, the vortex lattice orients itself parallel to the twin boundary and we observe the creation of a flux gradient and vortex free region near the edges of the twin boundary. For increasing drive, we find evidence for several distinct dynamical flow phases which we characterize by the density of defects in the vortex lattice, the microscopic vortex flow patterns, and orientation of the vortex lattice. We show that these different dynamical phases can be directly related to microscopically measurable voltage - current V(I) curves and voltage noise. By conducting a series of simulations for various twin boundary parameters we derive several vortex dynamic phase diagrams.Comment: 5 figures, to appear in Phys. Rev.