Magnetic-dipole induced appearance of vortices in a bilayered superconductor/soft-magnet heterostructure

The penetration of the magnetic field of an infinitesimal magnetic dipole into a bilayered type-II superconductor/soft-magnet heterostructure is studied on the basis of the classical London approach. The critical values of the dipole moment for the first appearance of a single magnetic vortex and, respectively, a magnetic vortex-antivortex pair in the superconductor constituent are obtained, when the magnetic dipole faces the superconductor or the soft-magnet constituent. This reveals that the soft-magnet constituent inhibits penetration of vortices into the superconductor constituent, when the dipole faces the soft-magnet constituent.Comment: 2 pages, 1 figure; accepted in Physica C for the special issue of Preceedings of the 8th Int. Conference on Materials and Mechanisms of Superconductivity and High Temperature Superconductors (M2S-HTSC), Dresden, Germany, July 9-14, 200

Magnetic detectability of a finite size paramagnet/superconductor cylindrical cloak

Cloaking of static magnetic fields by a finite thickness type-II superconductor tube surrounded by a coaxial paramagnet shell is studied. On the basis of exact solutions to the London and Maxwell equations, it is shown that perfect cloaking is realizable for arbitrary geometrical parameters including the thin film case for both constituents. In contrast to previous approximate studies assuming perfect diamagnetism of the superconductor constituent, it is proven that cloaking provides simultaneously full undetectability, that is the magnetic moment of the structure completely vanishes as well as all high-order multipole moments as soon as the uniform field outside remains unaffected.Comment: 6 pages, 2 figures, to be published in Applied Physics Letter

Virgin magnetization of a magnetically shielded superconductor wire: Theory and experiment

On the basis of exact solutions to the London equation, the magnetic moment of a type II superconductor filament surrounded by a soft-magnet environment is calculated and the procedure of extracting the superconductor contribution from magnetic measurements is suggested. A comparison of theoretical results with experiments on MgB2/Fe wires allows the estimation of the value of critical current for the first magnetic flux penetration

Magnetic cloaking by a paramagnet/superconductor cylindrical tube in the critical state

Cloaking of static magnetic fields by a finite thickness type-II superconductor tube being in the full critical state and surrounded by a coaxial paramagnet shell is studied. On the basis of exact solutions to the Maxwell equations, it is shown that, additionally to previous studies assuming the Meissner state of the superconductor constituent, perfect cloaking is still realizable at fields higher than the field of full flux penetration into the superconductor and for arbitrary geometrical parameters of both constituents. It is also proven that simultaneously the structure is fully undetectable under the cloaking conditions. Differently from the case of the Meissner state the cloaking properties in the application relevant critical state are realized, however, only at a certain field magnitude.Comment: 5 pages, 4 figures; to be published in Applied Physics Letters. arXiv admin note: substantial text overlap with arXiv:1401.356

Self-consistent model of unipolar transport in organic semiconductor diodes: accounting for a realistic density-of-states distribution

A self-consistent, mean-field model of charge-carrier injection and unipolar transport in an organic semiconductor diode is developed utilizing the effective transport energy concept and taking into account a realistic density-of-states distribution as well as the presence of trap states in an organic material. The consequences resulting from the model are discussed exemplarily on the basis of an indium tin oxide/organic semiconductor/metallic conductor structure. A comparison of the theory to experimental data of a unipolar indium tin oxide/poly-3-hexyl-thiophene/Al device is presented.Comment: 6 pages, 2 figures; to be published in Journal of Applied Physic

Vortex structure of thin mesoscopic disks in the presence of an inhomogeneous magnetic field

The vortex states in a thin mesoscopic disk are investigated within the phenomenological Ginzburg-Landau theory in the presence of different ''model'' magnetic field profiles with zero average field which may result from a ferromagnetic disk or circulating currents in a loop near the superconductor. We calculated the dependences of both the ground and metastable states on the magnitude and shape of the magnetic field profile for different values of the order parameter angular moment, i.e. the vorticity. The regions of existence of the multi-vortex state and the giant vortex state are found. We analysed the phase transitions between these states and studied the contribution from ring-shaped vortices. A new transition between different multi-vortex configurations as the ground state is found. Furthermore, we found a vortex state consisting of a central giant vortex surrounded by a collection of anti-vortices which are located in a ring around this giant vortex. The limit to a disk with an infinite radius, i.e. a film, will also be discussed. We also extended our results to ''real'' magnetic field profiles and to the case in which an external homogeneous magnetic field is present.Comment: 17 pages, 23 figures. Submitted to PR

Self-consistent analytical solution of a problem of charge-carrier injection at a conductor/insulator interface

We present a closed description of the charge carrier injection process from a conductor into an insulator. Common injection models are based on single electron descriptions, being problematic especially once the amount of charge-carriers injected is large. Accordingly, we developed a model, which incorporates space charge effects in the description of the injection process. The challenge of this task is the problem of self-consistency. The amount of charge-carriers injected per unit time strongly depends on the energy barrier emerging at the contact, while at the same time the electrostatic potential generated by the injected charge- carriers modifies the height of this injection barrier itself. In our model, self-consistency is obtained by assuming continuity of the electric displacement and the electrochemical potential all over the conductor/insulator system. The conductor and the insulator are properly taken into account by means of their respective density of state distributions. The electric field distributions are obtained in a closed analytical form and the resulting current-voltage characteristics show that the theory embraces injection-limited as well as bulk-limited charge-carrier transport. Analytical approximations of these limits are given, revealing physical mechanisms responsible for the particular current-voltage behavior. In addition, the model exhibits the crossover between the two limiting cases and determines the validity of respective approximations. The consequences resulting from our exactly solvable model are discussed on the basis of a simplified indium tin oxide/organic semiconductor system.Comment: 23 pages, 6 figures, accepted to Phys.Rev.

The Bean model of the critical state in a magnetically shielded superconductor filament

We study the magnetization of a cylindrical type-II superconductor filament covered by a coaxial soft-magnet sheath and exposed to an applied transverse magnetic field. Examining penetration of magnetic flux into the superconductor core of the filament on the basis of the Bean model of the critical state, we find that the presence of a non-hysteretic magnetic sheath can strongly enhance the field of full penetration of magnetic flux. The average magnetization of the superconductor/magnet heterostructure under consideration and hysteresis AC losses in the core of the filament are calculated as well.Comment: 4 pages, 3 figures; Proceedings of the 7th European Conference on Applied Superconductivity, Vienna, Austria, September 11-15, 200