Fermi surfaces of iron pnictides investigated by use of magnetic quantum oscillations

• Applicant: Professor Dr. Joachim Wosnitza
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2010 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 168450307

• Final Report Year: 2017

Final Report Abstract

In this project, superconducting phase diagrams as well as the Fermi-surface topologies and band-structure parameters of iron pnictides and their analogues were investigated. Our comprehensive de Haas–van Alphen studies of the nonsuperconducting 122 materials LaFe2 P2 and BaIr2 P2 in magnetic fields up to 34 T combined with state-of-the-art bandstructure calculations allowed to reveal detailed pictures of the Fermi-surface topologies. Compared to other 122 Fe-based superconductors, we find for both compounds that the electron-like Fermi-surface cylinder in the Brillouin-zone corner persists, whereas a holelike cylinder is absent. In spite of significant mass enhancements, pointing to strongly coupled Cooper pairs, no superconductivity is found which can be explained by the absence of sufficient nesting between the electron and hole parts of the Fermi surface. Additionally, we improved our existing setups for the modulation-field and cantilevertorque technique. We further designed and built a setup for measuring magnetic-torque in pulsed magnetic fields using piezo-resistive micro-cantilevers together with a dedicated rotator and custom-built amplifier bridge.

Publications

• Electron transport and anisotropy of the upper critical magnetic field in a Ba0.68 K0.32 Fe2 As2 single crystal, JETP Letters 93, 26 (2011) [Pis’ma v ZhETF 93, 29 (2011)]
  V. B. Gasparov, F. Wolff-Fabris, D. l. Sun, C. T. Lin, and J. Wosnitza
  
• Upper Critical Magnetic Field in Ba0.68 K0.32 Fe2 As2 and Ba(Fe0.93 Co0.07 )2 As2 , JETP Letters 93, 667 (2011) [Pis’ma v ZhETF 93, 746 (2011)]
  V. A. Gasparov, L. Drigo, A. Audouard, D. L. Sun, C. T. Lin, S. L. Bud’ko, P. C. Canfield, F. Wolff-Fabris, and J. Wosnitza
  
• Fermi-surface topology of the iron pnictide LaFe2 P2 , Phys. Rev. B 89, 220505(R) (2014)
  S. Blackburn, B. Prévost, M. Bartkowiak, O. Ignatchik, A. Polyakov, T. Förster, M. Côté, G. Seyfarth, C. Capan, Z. Fisk, R. G. Goodrich, I. Sheikin, H. Rosner, A. D. Bianchi, and J. Wosnitza
  
• Fermi surface of the superconductor BaIr2 P2 , Phys. Rev. B 92, 134518 (2015)
  T. Förster, B. Bergk, O. Ignatchik, M. Bartkowiak, S. Blackburn, M. Côté, G. Seyfarth, N. Berry, Z. Fisk, I. Sheikin, A. D. Bianchi, and J. Wosnitza