Thin film deposition and high-field transport properties of Fe-based superconductors
Karlsruhe Institute of Technology, Institute for Technical Physics, Karlsruhe Germany
The Fe-based superconductors (FBS) are very interesting materials both for basic research as well as in view of potential applications. FBS are unconventional, anisotropic, partially quantum-critical, multi-band superconductors, and all of these characteristics reflect to some extend in the electrical transport properties. They usually show very high upper critical fields and concurrent high irreversibility fields at low temperatures. This opens the possibility of high in-field critical current densities Jc, interesting especially for high-field applications.
Three crystallographic systems of FBS, namely the ‘11’ chalcogenides Fe(Se,Te), the ‘122’ pnictides BaFe2As2 with different kinds of doping, and the ‘1111’ oxypnictides REFeAs(O,F) (RE Sm, Nd), differing in critical temperature Tc and complexity of crystal structure, are often regarded for applications and readily prepared as thin films by pulsed laser deposition (PLD) or molecular beam epitaxy (MBE) on single-crystalline and technical substrates. Pauli limitation and multi-band effects lead to a strong temperature-dependent anisotropy of Hc2, which is furthermore different from the penetration depth anisotropy. This has to be taken into account for microscopic explanations of the Jc anisotropy. Short coherence lengths (similar to the cuprates) necessitate reasonably sharp textures (where nonetheless grain boundaries are pinning-active) and a complex landscape of nanoscale pinning centers for high current densities.
In this presentation, relationships among the three aforementioned systems (and others, such as LiFeAs and the intercalated systems), characteristics of their preparation as thin films, as well as their high-field transport properties will be discussed, mainly on the basis of selected examples of our group’s investigations in Fe-based superconducting thin films of the past 10 years.
Dr. Jens Hänisch is a group leader in Superconducting Films at KIT Karlsruhe, Germany. After completing his PhD in 2005 at the IFW Dresden and TU Dresden, Germany, he was a postdoc at Los Alamos National Laboratory before joining the faculty as a Senior Scientist at the IFW Dresden, Germany in 2008. His main research is devoted to application-oriented basic research on preparation of cuprate and Fe-based superconducting films with focus on microstructure-property correlations. Special interests and achievements in pinning improvement in HTS thin films, transport properties of Fe-based superconducting thin films and grain boundaries (GB) and GB networks in cuprate and iron-based high-temperature superconducting thin films. Among the prizes he has received in his career are the Outstanding Postdoctoral Presentation at the Los Alamos National Laboratory Symposium Championing Scientific Carriers (2006), Superconductivity Technology Center Spot Award for Achievements in DoE Coated Conductor Program(2008), and IOP Outstanding Reviewer for Superconductor Science and Technology(2016).