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[en] Following some prehistory, we discuss the steps leading to the Abrikosov vortex lattice and type-II superconductivity. Dissipation due to flux flow and flux creep represented an important discovery and leads to the strong interest in magnetic flux pinning. High-temperature superconductors and pancake vortices started the new concepts of vortex matter. Nonlinear effects at high vortex velocities, flux-flow instabilities, and some resulting open questions are discussed.
[en] Ohm's law with the linear relation between resistive voltage and electric current is strictly valid only in the limit of infinitesimally small voltages. On the other hand, at finite electric voltages nonlinearities in the electric resistance can develop due to the energy picked up by the charge carriers in the electric field. This can lead to important effects both in the case of semiconductors and of superconductors, where the energy rise of the charge carriers or the quasiparticles can become relatively large. In this paper we limit our discussion to the flux-flow voltage in the mixed state of a type-II superconductor. At sufficiently low temperatures the energy dependence of the quasiparticle density of states and, hence, of the quasiparticle scattering rate can cause distinct nonlinear effects in the flux-flow resistance. The recent advances in thin-film sample preparation provided new opportunities for observing nonlinear effects of the latter kind.