Abstract
Absence of macroscopic resistance is the most essential trait of superconductors for their practical applications. Yet several mechanisms lead to dissipation in the superconducting state such as weak links, fluctuations, and the motion of flux vortices in the mixed state of type II materials. Thus it is of practical as well as fundamental interest to explore these mechanisms to the fullest extent and to learn how to control them. Regarding the control of flux motion, most research efforts aim at preventing flux motion by introducing a variety of pinning strategies. In the present work, we discuss the circumstances under which it is possible to exclude vortices in the first place, or to short their motion through intrinsic multi-band effects. Experimental results on two model systems, molybdenum-germanium and magnesium diboride films, are presented to support these strategies.
Highlights
The transport of electrical current and levitation are two of the most important areas of practical importance for the application of superconductors
Superconductivity for energy applications is mainly concerned with the latter property, as it depends on the ability to carry lossless electrical currents for the purpose of power transmission and for the construction of extremely powerful electromagnets for use in generators and motors, and for other applications such as highenergy particle accelerators and nuclear fusion where intense magnetic fields are required
We show here one example each for the two sets of special conditions: the vortex-explosion scenario and the two-band mixed state with delocalized electric fields
Summary
The transport of electrical current and levitation are two of the most important areas of practical importance for the application of superconductors. These are based respectively on the two most important fundamental properties of the superconducting state: flux expulsion through the Meissner effect and the vanishing of resistance. A type-II superconductor enters the mixed state in the presence of a magnetic field B that is higher than the lower critical field Bc1 This mixed state consists of quantized flux vortices each containing a quantum of mag-. The motion of the vortices leads to an electric field within the superconductor and resistance and power dissipation, rendering the conductor unattractive for lossless current carrying applications. We discuss here some intrinsic fundamental phenomena that can alleviate the ill effects of vortex motion
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