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.

Universal scaling features of polarization switching are established experimentally in rather different classes of disordered ferroelectrics: in well-studied lead-zirconate titanate (PZT) ferroelectrics, in recently synthesized Custabilized 0.94(Bi 1/2 Na 1/2 )TiO 3 -0.06BaTiO 3 (BNT-BT) relaxor ferroelectrics, and in classical organic ferroelectrics P(VDF-TrFE). These scaling properties are explained by an extended concept of an inhomogeneous fi eld mechanism (IFM) of polarization dynamics in ferroelectrics. Accordingly, disordered ferroelectrics exhibit a wide spectrum of characteristic switching times due to a statistical distribution of values of the local electric fi eld. How this distribution can be extracted from polarization measurements is demonstrated. Generally, it is shown that the polarization response is primarily controlled by the statistical characteristics of disorder rather than by a temporal law of the local polarization switching.

The vortex state in a thin mesoscopic disk surrounded by a medium which enhances surface superconductivity is investigated theoretically in the framework of the phenomenological Ginzburg-Landau theory. We calculated the dependences of both the ground and metastable states on an external magnetic field perpendicular to the disk plane for different values of the order parameter angular moment, i.e., the vorticity. The magnetic field-temperature phase diagram is obtained and the regions of existence of the multivortex state and the giant vortex state are found. We analyzed the phase transitions between these states. Our results are also applicable for the analysis of the vortex state in extreme type-II mesoscopic disks.

Numerical simulations of a type-II superconducting wire subject to an ac transport current and oscillating transverse magnetic field are performed using the theory of the critical state. Time-dependent distributions of the current and the density of magnetic flux, the local power dissipation, and cycles of the magnetic moment are displayed. Noticeable inhomogeneous dissipation and field distortions are exposed. Results for hysteretic ac losses are reported too, and significant differences to predictions of available approximate formulae identified. Finally, a distinct low-pass filtering effect intrinsic to the wire’s magnetic response is revealed.

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 injectionlimited 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.