659 research outputs found

### Enhancement of vortex pinning in superconductor/ferromagnet bilayers via angled demagnetization

We use local and global magnetometry measurements to study the influence of
magnetic domain width w on the domain-induced vortex pinning in
superconducting/ferromagnetic bilayers, built of a Nb film and a ferromagnetic
Co/Pt multilayer with perpendicular magnetic anisotropy, with an insulating
layer to eliminate proximity effect. The quasi-periodic domain patterns with
different and systematically adjustable width w, as acquired by a special
demagnetization procedure, exert tunable vortex pinning on a superconducting
layer. The largest enhancement of vortex pinning, by a factor of more than 10,
occurs when w ~ 310 nm is close to the magnetic penetration depth.Comment: 5 pages, 3 figures, accepted to Phys. Rev. B, Rapid Communication

### Parton Branching in Color Mutation Model

The soft production problem in hadronic collisions as described in the
eikonal color mutation branching model is improved in the way that the initial
parton distribution is treated. Furry branching of the partons is considered as
a means of describing the nonperturbative process of parton reproduction in
soft interaction. The values of all the moments, and $C_q$, for q=2,...,5,
as well as their energy dependences can be correctly determined by the use of
only two parameters.Comment: 8 pages (LaTeX) + 2 figures (ps files), submitted to Phys. Rev.

### Tuning Vortex Confinement by Magnetic Domains in a Superconductor/Ferromagnet Bilayer

We use a line of miniature Hall sensors to study the effect of magnetic-domain-induced vortex confinement on the flux dynamics in a superconductor/ferromagnet bilayer. A single tunable bilayer is built of a ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy and a superconducting Nb layer, with the insulating layer in-between to avoid the proximity effect. The magnetic-domain patterns of various geometries are reversibly predefined in the Co/Pt multilayer using the appropriate magnetization procedure. The magnetic-domain geometry strongly affects vortex dynamics, leading to geometry-dependent trapping of vortices at the sample edge, nonuniform flux penetration, and strongly nonuniform critical current density. With the decreasing temperature, the magnetic pinning increases, but this increase is substantially weaker than that of the intrinsic pinning. The analysis of the initial flux penetration suggests that vortices may form various vortex structures, including disordered Abrikosov lattice or single and double vortex chains, in which minimal vortex-vortex distance is comparable to the magnetic penetration depth

### Tuning Vortex Confinement by Magnetic Domains in a Superconductor/Ferromagnet Bilayer

We use a line of miniature Hall sensors to study the effect of magnetic-domain-induced vortex confinement on the flux dynamics in a superconductor/ferromagnet bilayer. A single tunable bilayer is built of a ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy and a superconducting Nb layer, with the insulating layer in-between to avoid the proximity effect. The magnetic-domain patterns of various geometries are reversibly predefined in the Co/Pt multilayer using the appropriate magnetization procedure. The magnetic-domain geometry strongly affects vortex dynamics, leading to geometry-dependent trapping of vortices at the sample edge, nonuniform flux penetration, and strongly nonuniform critical current density. With the decreasing temperature, the magnetic pinning increases, but this increase is substantially weaker than that of the intrinsic pinning. The analysis of the initial flux penetration suggests that vortices may form various vortex structures, including disordered Abrikosov lattice or single and double vortex chains, in which minimal vortex-vortex distance is comparable to the magnetic penetration depth

### Fermi level dependence of magnetism and magnetotransport in the magnetic topological insulators Bi$_{2}$Te$_{3}$ and BiSbTe$_{3}$ containing self-organized MnBi$_{2}$Te$_{4}$ septuple layers

The magnetic coupling mechanisms underlying ferromagnetism and
magnetotransport phenomena in magnetically doped topological insulators have
been a central issue to gain controlled access to the magneto-topological
phenomena such as quantum anomalous Hall effect and topological axion
insulating state. Here, we focus on the role of bulk carriers in magnetism of
the family of magnetic topological insulators, in which the host material is
either Bi$_{2}$Te$_{3}$ or BiSbTe$_{3}$, containing Mn self-organized in
MnBi$_{2}$Te$_{4}$ septuple layers. We tune the Fermi level using the electron
irradiation technique and study how magnetic properties vary only through the
change in carrier density. Ferromagnetic resonance spectroscopy excludes bulk
magnetism based on a carrier-mediated process. Furthermore, the
magnetotransport measurements show that the anomalous Hall effect is dominated
by the intrinsic and dissipationless Berry-phase driven mechanism, with the
Hall resistivity enhanced near the bottom/top of the conduction/valence band,
due to the Berry curvature which is concentrated near the avoided band
crossings. These results demonstrate that the anomalous Hall effect can be
effectively managed, maximized, or turned off, by adjusting the Fermi level.Comment: 11 pages, 7 figure

### Generalized Relativistic Meson Wave Function

We study the most general, relativistic, constituent $q{\overline q}$ meson
wave function within a new covariant framework. We find that by including a
tensor wave function component, a pure valence quark model is now capable of
reproducing not only all static pion data ($f_\pi$, $\langle r_\pi^2 \rangle$)
but also the distribution amplitude, form factor $(F_\pi(Q^2))$, and structure
functions. Further, our generalized spin wave function provides a much better
detailed description of meson properties than models using a simple
relativistic extension of the $S=L=0$ nonrelativistic wave function.Comment: 17 pages, REXTeX 3.0 file, (uuencoded postscript files of 8 figures
appended

### A Color Mutation Model of Soft Interaction in High Energy Hadronic Collisions

A comprehensive model, called ECOMB, is proposed to describe multiparticle
production by soft interaction. It incorporates the eikonal formalism, parton
model, color mutation, branching and recombination. The physics is conceptually
opposite to the dynamics that underlies the fragmentation of a string. The
partons are present initially in a hadronic collision; they form a single,
large, color-neutral cluster until color mutation of the quarks leads to a
fission of the cluster into two color-neutral subclusters. The mutation and
branching processes continue until only $q\bar q$ pairs are left in each small
cluster. The model contains self-similar dynamics and exhibits scaling behavior
in the factorial moments. It can satisfactorily reproduce the intermittency
data that no other model has been able to fit.Comment: 24 pages including 11 figures in revtex epsf styl

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