At the edge of an unconventional quantum system: Physics and applications of interfaces involving high-Tc superconductors

Dr. Hans Hilgenkamp
Faculty of Science and Technology and MESA+ Research Institute
University of Twente, Enschede.

 In many applications of high-temperature superconductors, interfaces play a central role.
For example, on the one hand, electronic applications and highly sensitive SQUID sensors are based on Josephson junctions, whereas on the other hand large current applications have been strongly hampered by the strong current-blocking properties of grain boundaries in these materials.

For the interface properties, two basic aspects of high temperature superconductors play a crucial role, namely their sensitivity to interface charging effects and the unconventional d-wave symmetry of the superconducting state. In both aspects, the high-Tc cuprates differ essentially from their metallic, low-Tc counterparts.

With increasing knowledge about those aspects, also ways were found to ameliorate interface properties and to construct novel superconducting quantum-devices, with potential use in superconducting electronic circuitry.

Part of this development will be discussed in the presentation.  By the example of grain boundaries the basic concepts will be introduced. Subsequently a transition is made to novel structures based on interfaces between high-Tc and low-Tc superconductors. These show remarkable effects, including the spontaneous generation of magnetic half-flux quanta.