Exploring the Unusual Flux Pinning behavior in Ba-122

01.05.2016 - 31.12.2019
Research funding project
Insufficient pinning of magnetic flux vortices is still a hurdle for the application of high-temperature superconductors. While significant improvements have been obtained by optimizing the size, density, and morphology of pinning centers during the past years, the proposed project aims at boosting the critical current densities by charge doping. Recent results indicate that flux pinning can be significantly enhanced in non-conventional superconductors in the vicinity of a quantum critical point. In particular, magnetic quantum fluctuations or fluctuations of the crystal structure seem to be responsible for a sharp maximum in the critical current density as a function of doping concentration in BaFe2As2 (Ba-122) single crystals. In addition, an unusually high pinning efficiency was found at the doping concentration of the quantum critical point in a fast neutron irradiated crystal. These observations fuel the hope that quantum fluctuations can enhance flux pinning significantly in technical relevant superconductors. We will explore this hypothesis using Ba-122 samples with different doping. It is noteworthy, however, that quantum fluctuations also occur in other non-conventional superconductors such as the cuprates, which are currently most promising for applications of high-temperature superconductors. High quality single crystals of Co-, P-, and K-doped Ba-122 with a wide range of doping concentrations will be grown at the National Institute of Advanced Industrial Science and Technology (AIST, Japan). The superconducting properties will be assessed by magnetization and resistive measurements. The microstructure will be investigated by transmission electron microscopy and atom probe tomography. We will use two approaches to separate the influence of the pinning structure from effects of quantum fluctuations. First, a benchmark defect structure will be introduced into the crystals by means of fast neutron irradiation at TU Wien, which ¿overwrites¿ the defect structure in the pristine crystals and thus can be considered as equivalent at all doping concentrations. Second, magnetization measurements will be performed under high pressure at AIST, which leave the defect structure of the pristine crystals unchanged, while shifting the doping concentration at which the quantum critical points occur. Finally the application potential of our findings will be explored by a comprehensive analysis of the field and temperature dependence of the critical current densities, which will be optimized by artificially introduced pinning centers (e.g. BZO-nanoparticles). The project will be carried out by one PhD student under the supervision of Dr. Michael Eisterer at the Atominstitut of TU Wien. Dr. Hiroshi Eisaki will lead the efforts at AIST.

People

Project leader

Institute

Grant funds

  • FWF - Österr. Wissenschaftsfonds (National) Stand-Alone Project Austrian Science Fund (FWF) Call identifier I 2814-N36

Research focus

  • Special and Engineering Materials: 25%
  • Structure-Property Relationsship: 25%
  • Materials Characterization: 50%

Keywords

GermanEnglish
Hochtemperatursupraleitende MaterialienHigh temperature superconducting (HTS) materials

External partner

  • National Institute of Advanced Industrial Science and Technology

Publications