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Many potential applications of superconductors, such as for example high-field magnets,
transformers, generators, and motors, require high current densities and and high
magnetic fields at the same time. This limits the usefulness of the so-called high-temperature
superconductors (HTSC) at the from a crygenic point of view desirable temperature
of liquid nitrogen (77 K, -196oC). The reason lies in the general property
of type-II superconductors to allow a penetrating magnetic field in the form of quantized
magnetic flux lines and the complicated layered crystal structure of the cuprate HTSC.
An applied current excerpts a force on the flux lines which start to move unless there
is another force counter-acting the first one. Flux lines moving with an average velocity
v on the other hand result in an induced electrical field E proportional
to v in such a way that it reduces the applied current. In other words moving
flux lines result in electrical resistance. That resistance can be overcome by pinning
the flux lines at intrinsic or artificially introduced defects in the atomic structure
of the superconductor.
Two of the materials which look promising for cable and wire applications (known as
BSCCO-2212 and BSCCO-2223) have a pronounced layered crystal structure consisting of
alternating superconducting and insulating sheets. This layered structure makes it
very difficult to effectively pin the flux lines in these materials. In order to
maximize the current carrying capacity of these materials a comprehensive understanding
of the behavior of flux lines under different conditions such as magnetic field and
temperature is necessary. In my Ph.D. thesis I look at some aspects of this wide and
complicated subject in the case of a model system that allows to tune certain parameters
which are difficult to change in other materials.
Go to the downloads page for a pdf-version of the thesis or parts of it.
Related Publications (pdf usually requires subscription)
- A. Engel and H. J. Trodahl, Vortex dynamics and states of artificially layered superconducting films with correlated defects, Phys. Rev. B 66, 184505 (2002) (abstract, pdf)
- A. Engel, H. J. Trodahl, A. Markwitz and V. J. Kennedy, Characterization of superconducting multilayered films using RBS and TEM, Mod. Phys. Lett. B, 15, 1314 (2001) (abstract, pdf)
- A. Engel, H. J. Trodahl, J. C. Abele and S. M. Robinson, Flux pinning and phase diagrams in amorphous Ta0.3Ge0.7/Ge multilayers with coplanar defects, Phys. Rev. B, 63, 184502 (2001) (abstract, pdf)
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