Charge carrier injection into insulating media: single-particle versus mean-field approach

Self-consistent, mean-field description of charge injection into a dielectric medium is modified to account for discreteness of charge carriers. The improved scheme includes both the Schottky barrier lowering due to the individual image charge and the barrier change due to the field penetration into the injecting electrode that ensures validity of the model at both high and low injection rates including the barrier dominated and the space-charge dominated regimes. Comparison of the theory with experiment on an unipolar ITO/PPV/Au-device is presented.Comment: 32 pages, 9 figures; revised version accepted to PR

Nucleation of superconductivity and vortex matter in superconductor - ferromagnet hybrids

The theoretical and experimental results concerning the thermodynamical and low-frequency transport properties of hybrid structures, consisting of spatially-separated conventional low-temperature superconductor (S) and ferromagnet (F), is reviewed. Since the superconducting and ferromagnetic parts are assumed to be electrically insulated, no proximity effect is present and thus the interaction between both subsystems is through their respective magnetic stray fields. Depending on the temperature range and the value of the external field H_{ext}, different behavior of such S/F hybrids is anticipated. Rather close to the superconducting phase transition line, when the superconducting state is only weakly developed, the magnetization of the ferromagnet is solely determined by the magnetic history of the system and it is not influenced by the field generated by the supercurrents. In contrast to that, the nonuniform magnetic field pattern, induced by the ferromagnet, strongly affect the nucleation of superconductivity leading to an exotic dependence of the critical temperature T_{c} on H_{ext}. Deeper in the superconducting state the effect of the screening currents cannot be neglected anymore. In this region of the phase diagram various aspects of the interaction between vortices and magnetic inhomogeneities are discussed. In the last section we briefly summarize the physics of S/F hybrids when the magnetization of the ferromagnet is no longer fixed but can change under the influence of the superconducting currents. As a consequence, the superconductor and ferromagnet become truly coupled and the equilibrium configuration of this "soft" S/F hybrids requires rearrangements of both, superconducting and ferromagnetic characteristics, as compared with "hard" S/F structures.Comment: Topical review, submitted to Supercond. Sci. Tech., 67 pages, 33 figures, 439 reference

Inverse-gas chromatography and the thermodynamics of sorption in polymers

In this review, the development of inverse gas chromatography (IGC) is briefly described, the role of A.A. Tager's studies is indicated, and the principles of using the IGC method to solve problems of the ther- modynamics of sorption of gases and vapors in polymers are formulated. The IGC method was originally developed by Guillet's school to study the thermodynamics of sorption in polymers above their glass-transi- tion temperatures; later, it was generalized and extended to the study of sorption processes below the glass- transition temperature in high-fractional free-volume polymers. These polymers exhibit specific features, such as strong exothermicity of mixing (Hm), dependence of ?Hm on the size of the sorbate molecule, and high solubility coefficients. Chromatographic studies of sorption in the AF1600 amorphous perfluori- nated polymer above and below its glass-transition temperature made it possible to test a new thermodynamic model that describes the sorption of gases and vapors in glassy polymers. © Pleiades Publishing, Ltd., 2012